Thermoformed polypropylene mineral-filled microwaveable containers having food contact compatible olfactory properties and process for their manufacture

ABSTRACT

Low-odor microwaveable mineral-filled polypropylene food contact articles are disclosed. The articles are prepared by low temperature processing and typically include odor-suppressing basic organic or inorganic compounds. Preferably, the articles are substantially free from C8 and C9 organic ketones associated with undesirable odors. Further improvements to the articles include crack-resistant embodiments with synergistic amounts of polyethylene and titanium dioxide.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. patentapplication Ser. No. 09/267,716, filed Mar. 12, 1999 entitledDISPOSABLE, MICROWAVEABLE CONTAINERS HAVING SUITABLE FOOD CONTACTCOMPATIBLE OLFACTORY PROPERTIES AND PROCESS FOR THEIR MANUFACTURE whichwas a non-provisional patent application based on U.S. Provisionalpatent application Ser. No. 60/078,923, filed Mar. 20, 1998 alsoentitled DISPOSABLE, MICROWAVEABLE CONTAINERS HAVING SUITABLE FOODCONTACT COMPATIBLE OLFACTORY PROPERTIES AND PROCESS FOR THEIRMANUFACTURE, the priority of which applications is hereby claimed.

BACKGROUND OF THE INVENTION

[0002] Filled polypropylene articles have been observed to exhibitundesirable odors, particularly upon heating. In this respect, see U.S.Pat. No. 5,023,286 to Abe et al., wherein phenolic antioxidants aresuggested to control the odor problem. Other polypropylene compositionsmay be found in U.S. Pat. Nos. 4,734,450 to Kawai et al.; U.S. Pat. No.5,045,369 to Kobayashiet al.; U.S. Pat. No.5,300,747 of Simon; U.S. Pat.No. 5,439,628 of Huang and U.S. Pat. No. 4,933,526 of Fisher et al.

[0003] This invention relates to disposable, mineral-filledpolypropylene microwaveable containers having suitable food contactcompatible olfactory properties including cups, trays, soufflé dishes,lids, plates, bowls, and related articles of manufacture useful forpreparation, storage, delivery, and serving of food, wherein convenienceand low cost are of paramount importance. Nevertheless, suitable foodcontact compatible olfactory properties, appearance, and tactilecharacteristics of the plate, container, etc., are important forconsumer preference. The suitability of these disposable articles ofmanufacture for microwave cooking, or heating of food, has an importantplace in today's marketplace. Both the commercial and retail marketcomponents need an aesthetically pleasing microwaveable, disposable,rigid and strong container, plate, or cup, and related articles ofmanufacture which also have suitable food contact compatible olfactoryproperties. These disposable microwaveable containers and plates furtherexhibit a melting point of no less than about 250° F., the containers orplates being dimensionally stable and resistant to grease, sugar andwater at temperatures up to at least 220° F. and exhibiting sufficienttoughness to be resistant to cutting by serrated polystyrene flatware.

SUMMARY OF THE INVENTION

[0004] Microwaveable, disposable, rigid and strong containers and plateshaving suitable food contact compatible olfactory properties have beenprepared. These disposable and microwaveable articles of manufactureexhibit (a) suitable food contact compatible olfactory properties; and(b) a melting point of not less than 250° F., suitably 250° F. to 330°F. In preferred embodiments these articles of manufacture exhibit amicronodular surface on the side coming in contact with food. Thesemicrowaveable, food contact compatible containers and plates aredimensionally stable and resistant to grease, sugar and water attemperatures of at least 220° F. and are of sufficient toughness to beresistant to cutting by serrated polystyrene flatware. The containersand plates of this invention answer a long felt need for products whichcan withstand the severe conditions of a microwave oven when commonfoods such as beans and pork, pancakes with syrup, pepperoni pizza, andbroccoli with cheese are microwaved during food cooking andreconstituting processes.

[0005] It has been found in accordance with the present invention thatmineral-filled polypropylene food contact articles such as bowls orplates exhibit superior olfactory characteristics when preparedincluding a basic organic or inorganic compound.

[0006] There is provided in a first aspect of the present invention amethod of preparing a microwaveable, mineral-filled polypropylene foodcontact article including the steps of: (a) preparing a melt-compoundedcomposition with from about 40 to 90 percent by weight of apolypropylene polymer; from about 10 to about 50 percent by weight of aprimary mineral filler and an effective odor-reducing amount of a basicorganic or inorganic compound, the melt-compounded compositon exhibitingan odor index of less than about 0.75; (b) extruding the aforesaid meltcomounded composition into sheet form; and (c) forming the food contactarticle from the sheet, wherein the basic organic or inorganic compoundis operative to reduce undesireable odors in the melt-compoundedcomposition to the aforesaid odor index value of 0.75 or less. Theprimary filler is mica, clay, a siliceous material, ceramics, glass, asulfate mineral, or mixtures thereof.

[0007] Typically, the primary mineral filler is mica, talc, kaolin,bentonite, wollastonite, milled glass fiber, glass beads (solid orhollow), silica, or silicon carbide whiskers or mixtures thereof. Wehave discovered that when polypropylene is melt-compounded withacidic-type minerals the resulting mixture has a higher odor index(offensive odors) that would disqualify them from use in food serviceproducts.

[0008] Acidic type fillers such as mica; natural clay minerals such askaolinite, bentonite, attapulgite, montmorillonite, clarite, or fuller'searth; and silica are particularly detrimental in generating odorcompounds when processed under high shear and high temperatureconditions experienced during twin screw compounding. We have found thatchanging the compounding process and adding a basic component to theprimary acidic filler allows the production of low odor index compounds.The reason for this effect is unknown since the fundamental cause of thedegradation in polypropylene may be due, in part, to catalysis effectscaused by impurities in the mineral as well as its acidic or basicnature. In this regard, the addition of CaCo₃ to talc is beneficialwhereas, it may be unnecessary when wollastonite is used as the primaryfiller.

[0009] The preferred primary fillers are mica, talc, kaolin, bentonite,milled glass fibers, and wollastonite or mixtures thereof Of thesemilled glass fibers and wollastonite are basic in nature and may notnecessarily require the addition of a secondary basic component.

[0010] As noted above, suitable mineral fillers include mica, talc,kaolin, bentonite, wollastonite, milled glass fiber, glass beads (hollowor solid), silica whiskers, silicon carbide whiskers and mixturesthereof as well as the mineral fillers recited herein, whereas the basicorganic or inorganic compound is generally the reaction product of analkali metal or alkaline earth element with carbonates, phosphates,carboxylic acids as well as alkali metal and alkaline earth elementoxides, hydroxides, or silicates and basic metal oxides includingmixtures of silicon dioxide with one or more of the following oxides:magnesium oxide, calcium oxide, barium oxide, and mixtures of theforegoing. More specifically, the basic organic or inorganic compoundmay be selected from the group consisting of: calcium carbonate, sodiumcarbonate, potassium carbonate, barium carbonate, aluminum oxide, sodiumsilicate, sodium borosilicate, magnesium oxide, strontium oxide, bariumoxide, zeolites, sodium citrate, potassium citrate, calcium stearate,potassium stearate, sodium phosphate, potassium phosphate, magnesiumphosphate, mixtures of silicon dioxide with one or more of the followingoxides: magnesium oxide, calcium oxide, barium oxide, and mixtures ofone or more of the above. Furthermore, hydroxides of the metals andalkaline earth elements recited above may be utilized.

[0011] Where a basic inorganic odor suppressing compound is chosen,generally such compound is selected from the group consisting of calciumcarbonate, sodium carbonate, potassium carbonate, barium carbonate,aluminum oxide, sodium silicate, sodium borosilicate, magnesium oxide,strontium oxide, barium oxide, zeolites, sodium phosphate, potassiumphosphate, magnesium phosphate, mixtures of silicon dioxide with one ormore of the following oxides: magnesium oxide, calcium oxide, bariumoxide, and mixtures of one or more of the basic inorganic compounds setforth above. The amount of a basic inorganic compound is generally fromabout 2 to 20 weight percent, but is usually from about 5 to about 15weight percent of the article. Most preferably the basic inorganiccompound selected is calcium carbonate; typically present from about 5to about 20 weight percent.

[0012] Where an organic compound is chosen, it is typically selectedfrom the group consisting of sodium stearate, calcium stearate,potassium stearate, sodium citrate, potassium citrate, and mixtures ofthese where the amount of such compound is from about 0.5 to about 2.5weight percent of the article.

[0013] Typically, microwaveable articles produced in accordance with thepresent invention exhibit an odor index of less than about 0.75;preferably less than about 0.6; with a practical lower limit being 0.1or so.

[0014] As shown below in connection with microwaveability testing, andsummarized in Table 20, competing commercial polystyrene type platescannot withstand the high temperatures generated in the microwave ovenduring food contact and either significantly warp or deform when theaforementioned food products were heated on them. Under the usualmicrowaving conditions with high grease content foods, the prior artplates tend to deform and flow to the point where parts of the platebecome adhered to the inside of the microwave oven. For disposableplates and containers, having suitable food contact olfactoryproperties, appearance and feel are important attributes. Anothersignificant property of the containers and plates of this invention istheir cut resistance. These rigid articles of manufacture are ofsufficient toughness to be resistant to cutting by serrated polystyreneflateware. In normal usage they are also resistant to cutting by regularmetal flatware.

[0015] Whereas any microwaveable article may be produced in accordancewith the invention, most typically the article is a bowl or a platesuitable for serving food at a meal. Preferred articles are thermoformedand include a micronodular food contact surface. Micronodular foodcontact surfaces are produced by thermoforming a sheet into the articlewhich has been extruded optionally with at least one matte roll and byvacuum thermoforming the sheet by applying vacuum opposite to thesurface where the micronodular surface is desired. Most typically themicronodular surface will have a surface gloss of less than about 35 at75° as measured by TAPPI method T-480-OM 92. Articles also willtypically have a Parker Roughness Value of at least about 12 microns.

[0016] While any suitable polypropylene polymer may be used, thepolypropylene polymers are preferably selected from the group consistingof isotactic polypropylene, and copolymers of propylene and ethylenewherein the ethylene moiety is less than about 10% of the units makingup the polymer, and mixtures thereof. Generally, such polymers have amelt flow index from about 0.3 to about 4, but most preferably thepolymer is isotactic polypropylene with a melt-flow index of about 1.5.In particularly preferred embodiments, the melt-compounded compositionfrom which the resultant extruded sheet is formed into articles furtherincludes a polyethylene component and titanium dioxide. The polyethylenecomponent may be any suitable polyethylene such as HDPE, LDPE, MDPE,LLDPE or mixtures thereof.

[0017] The various polyethylene polymers referred to herein aredescribed at length in the Encyclopedia of Polymer Science & Engineering(2d Ed.), Vol. 6; pp: 383-522, Wiley 1986; the disclosure of which isincorporated herein by reference. HDPE refers to high densitypolyethylene which is substantially linear and has a density ofgenerally greater that 0.94 up to about 0.97 g/cc. LDPE refers to lowdensity polyethylene which is characterized by relatively long chainbranching and a density of about 0.912 to about 0.925 g/cc. LLDPE orlinear low density polyethylene is characterized by short chainbranching and a density of from about 0.92 to about 0.94 g/cc. Finally,intermediate density polyethylene (MDPE) is characterized by relativelylow branching and a density of from about 0.925 to about 0.94 g/cc.Unless otherwise indicated these terms have the above meaning throughoutthe description which follows.

[0018] The microwaveable articles according to the invention typicallyexhibit melting points from about 250 to about 330° F. and include micaor other primary fillers in amounts from about 20 to about 35 weightpercent. Most preferably mica is present at about 30 weight percent, andcalcium carbonate is present from about 8 to about 12 weight percent.

[0019] It has been found that C8 and C9 organic ketones correlate wellwith or are associated with undesirable odors in polypropylene/micacompositions. Accordingly, it is preferred that articles in accordancewith the invention are substantially free from volatile C8 and C9organic ketones. In order to avoid undesirable odors, articles inaccordance with the invention are preferably prepared from amelt-compounded polyolefin mica composition which is prepared at aprocess melt temperature of less than about 425° F.; with below about400° F. being even more preferred. Optionally, the melt processedpolyolefin/mineral composition is melt-compounded in a nitrogenatmosphere.

[0020] In another aspect of the invention, there is provided athermoformed, mineral-filled polypropylene food contact article formedfrom a melt-compounded composition comprising from about 40 to about 90percent by weight of a polypropylene polymer, from about 10 to about 50percent by weight of a primary mineral filler and an effectiveodor-reducing amount of a basic organic or inorganic compound operativeto impart an odor index of less than about 0.75 to said melt-compoundedcomposition.

[0021] Preferably the inventive articles are prepared from amelt-compounded polyolefinimica composition prepared by way of a lowtemperature compounding process.

[0022] A preferred low temperature compounding process used forproducing mineral-filled polypropylene melt-compounded compositions withan odor index of less than about 0.75 including a basic odor suppressingagent in accordance with the invention with from about 40 to about 90percent by weight of a polypropylene polymer includes the sequentialsteps of: (a) preheating a polypropylene polymer while maintaining thepolymer below a maximum temperature of about 370° F. and preferablybelow 350° F. and more preferably below a maximum of about 260° F.; butsuitably above about 240° F.; followed by; (b) admixing mineral fillerto said preheated polymer in an amount from about 10 to about 50 percentweight based on the combined weight of the resin and primary filler andmaintaining the mixture below about 425° F.; followed by, (c) extrudingthe mixture. Polymer may be melted exclusively through the applicationof shear, or the shear may be supplemented through heating by infraredradiation or ordinary heating coils or performed externally to themixing chamber. Preferably, the basic odor suppressing agent is addedsimultaneously with the mineral filler

[0023] It is desirable to keep the duration of the step of admixingmineral filler and a basic odor suppressant agent to the mixturerelatively short so as not to generate compounds which cause odor and topreserve the particle size and aspect ratio of the mineral filler.Accordingly, the step of admixing the mineral filler should be no morethan about five minutes with the duration of the admixing step of lessthan about three minutes being even more preferred. Any suitable meansmay be used to carry out the sequential process in accordance with theinvention, however, the process is normally carried out in a batch modein a mixing chamber provided with a pair of rotating rotors in anapparatus referred to in the industry as a Banbury type mixer. One maychoose to use a twin screw extruder or a Buss kneader to practice theinventive process if so desired, provided that appropriate elements areused to minimize shear heating.

[0024] Thermoforming is typically conducted at a sheet temperature offrom about 260° to about 310° F., and more preferably at a temperatureof from about 280° to about 300° F.

[0025] There is provided in a still further aspect of the invention acrack-resistanit, thermoformed food contact article having a wallthickness ranging from about 10 to about 80 mils consisting essentiallyof from about 40 to about 90 weight percent of a polypropylene polymer,from about 10 to about 50 percent by weight of a mineral filler, fromabout 1 to about 15 percent by weight polyethylene, from about 0.1 toabout 5 weight percent titanium dioxide and optionally including a basicorganic or inorganic compound. The basic compound is, generallyspeaking, the reaction product of an alkali metal or alkaline earthelement with carbonates, phosphates, carboxylic acids as well as alkalimetal and alkaline earth element oxides, hydroxides, or silicates andbasic metal oxides, including mixtures of silicon dioxide with one ormore of the following oxides: magnesium oxide, calcium oxide, bariumoxide, and mixtures thereof. A particularly preferred article is wherethe basic organic or inorganic compound is calcium carbonate which ispresent in an amount of from about 5 to about 20 weight percent.

[0026] Polyethylene is more typically present from about 2.5 to about 15weight percent, preferably from about 4 to about 5 weight percent of thecrack resistant article.

[0027] Titanium dioxide is included in various amounts, from about 0.1to about 3 percent by weight being typical; from about 0.25 to 2 percenttitanium dioxide may be included. Preferably, titanium dioxide isincluded in at least 0.5 percent by weight.

[0028] The caliper, or wall thickness, of the articles is usually fromabout 0.010 to about 0.050 inches or from about 10 mils to 50 mils. Acaliper of from about 15 to 25 mils is most typically employed.

[0029] While any suitable polypropylene polymer may be employed, themost preferred polymer is isotactic polypropylene having a melt index inthe range of from about 0.3 to 4, with a melt index of about 1.5 beingtypical. The polyethylene employed may be HDPE, LLDPE, LDPE or MDPE,mixtures thereof or a polyethylene with bimodal molecular weightdistribution. Polypropylene is sometimes referred to hereafter as “PP”.

[0030] The inventive compositions from which the crack resistantarticles are made do not include coupling agents such as maleicanhydride containing polypropylene as further described herein, but mayoptionally include other components which do not alter the basic andnovel characteristics of the crack-resistant plates. For example,nucleants such as sodium benzoate in amounts detrimental to crackresistance are to be avoided.

[0031] In a still further aspect of the invention there is provided amethod of making a microwaveable mineral-filled polypropylene foodcontact article comprising preparing a melt-compounded compositioncomprising from about 40 to about 90 percent by weight of apolypropylene polymer and from about 10 to about 50 percent by weight ofa mineral filler and optionally an effective amount of an odor-reducingcompound. The melt-compounded composition exhibits a relative aromaindex, relative to a corresponding composition consisting essentially ofpolypropylene and mica of less than about 0.75. The composition isextruded into a sheet and formed into a suitable food contact article.Preferably, the article consists essentially of polymer and mineralfiller and excludes such components as excess anti-oxidants and thelike.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention will become more fuilly understood from thedetailed description given hereinbelow and the accompanying drawings,which are given by way of illustration only, and thus, are notlimitative of the present invention and wherein:

[0033]FIG. 1 is a schematic flow diagram of the sheet extrusion process;

[0034]FIG. 2 is a schematic flow diagram of the thermoforming processfor the manufacture of plates and containers having a micronodularsurface;

[0035]FIG. 3 is a chromatogram of extract from the Likens-Nickersonextraction from a melt processed polypropylene/mica compositionexhibiting relatively high odor;

[0036]FIG. 4 is a chromatogram of extract from the Likens-Nickersonextraction from a melt processed polypropylene/mica compositionexhibiting relatively low odor;

[0037]FIG. 5 is a plot of sensor responses vs. timie for an automatedaroma scanning device;

[0038]FIG. 6 is a plot of the response integrals for the 32 sensors inan aroma scanning device for 3 different polypropylene/micacompositions;

[0039]FIG. 7 is a schematic diagram of a Banbury type compounder;

[0040]FIG. 8 is a plot of current draw vs. time for a compoundingprocess according to the present invention in a compounder of the typeshown in FIG. 7:

[0041]FIG. 9A is a scanning electron photomicrograph of a plate (upperpicture) and FIG. 9B is a scaniing electron photomicrograph of a sheet(lower picture) of this invention wherein there is shown themicronodular food contact surface of the plate but not so for the neatextruded sheet;

[0042]FIG. 10 is a graph plotting gloss versus mica level;

[0043]FIG. 11 is a graph plotting the plate rigidity versus mica level;

[0044]FIG. 12A is a scanning electron photomicrograph of a sheet of thisinvention showing a matted surface and FIG. 12B is a scanning electronphotomicrograph of a non-matted surface;

[0045]FIGS. 13A and 13B are scanning electron photomicrographs of sheetsof this invention showing two high gloss sides;

[0046]FIGS. 14A and B are isometric drawings of a plate of thisinvention;

[0047]FIGS. 15A through C include cross sectional views of the plateshown in FIGS. 14A and B;

[0048]FIG. 16 is a radial cross-section of the plate shown in FIGS. 14Aand B;

[0049]FIG. 17 is a schematic profile of the plate shown in FIGS. 14A andB, beginning from the center line of the plate, formed in accordancewith the present invention;

[0050]FIG. 18 is a drawing of another plate of this invention;

[0051]FIG. 19 is a cross sectional view of the plate shown in FIG. 18;

[0052]FIG. 20 is a schematic profile of the plate shown in FIG. 18beginning from the center line;

[0053]FIGS. 21A and 21B are drawings of a tray included in thisinvention;

[0054]FIGS. 22 A, B and C include a cross sectional view of the trayshown in FIGS. 21A and B;

[0055]FIG. 23 is a radial cross section of the tray shown in FIGS. 21Aand B;

[0056]FIG. 24 is a schematic profile of the tray shown in FIGS. 21A andB beginning from the center line;

[0057]FIGS. 25A and B are drawings of a bowl of this invention;

[0058]FIGS. 26A through C include a cross-sectional view of the bowlshown in FIGS. 25A and B;

[0059]FIG. 27 is a radial cross section of the bowl shown in FIGS. 25Aand B;

[0060]FIG. 28 is a schematic profile of the bowl shown in FIGS. 25A andB beginning from the center line;

[0061]FIG. 29 is a drawing of a take-out food container included in thisinvention;

[0062]FIGS. 30A and B are drawings of another bowl of this invention;

[0063]FIGS. 31A through 31C include a cross-sectional view of the bowlshown in FIGS. 30A and 30B;

[0064]FIG. 32 is a radial cross section of the bowl shown in FIGS. 30Aand 30B;

[0065]FIG. 33 is a profile of the bowl shown in FIGS. 30A and 30B;

[0066]FIG. 34 is a graph comparing the rigidity of the plates of thisinvention with prior art commercial products in the context of currentmaterial costs; and

[0067]FIG. 35 is a bar graph comparing the heat resistance of the platesof this invention with prior art commercial products.

DETAILED DESCRIPTION OF THE INVENTION

[0068] The aesthetically pleasing microwaveable disposable, rigid andstrong containers including plates, bowls, cups, trays, buckets, souffledishes and lids comprise isotactic polypropylene, propylene-ethylenecopolymer, or blends of isotactic polypropylene and propylene-ethylenecopolymer coupled with a mixture of a primary inorganic mineral fillersuch as mica, clay and the like and basic inorganic or organic compoundswhich are the reaction product of an alkali metal or alkaline earthelement with carbonates, hydroxides, phosphates, carboxylic acids,mixtures of silicon dioxide with one or more of the following oxides:magnesium oxide, calcium oxide, barium oxide, and mixtures of one ormore of the basic organic or inorganic compounds set forth herein.

[0069] Suitably the basic inorganic or organic compounds are selectedfrom the group consisting of calcium carbonate, sodium carbonate,potassium carbonate, barium carbonate, aluminum oxide, sodium silicate,sodium borosilicate, magnesium oxide, strontium oxide, barium oxide,zeolites, sodium phosphate, potassium phosphate, magnesium phosphate,mixtures of silicon dioxide with one or more of the following oxides:magnesium oxide, calcium oxide, barium oxide, and mixtures of these orother basic inorganic or organic compounds such as sodium stearate,calcium stearate, potassium stearate, sodium citrate, potassium citrate,and mixtures of these basic organic compounds.

[0070] The function of the basic inorganic compound or organic compoundis to minimize the formation of odor-causing compounds in themineral-filled polyolefm composition and thus provide products with foodcontact compatible olfactory properties for consumer use. In thisconnection, the amount of the basic inorganic compound or organiccompound added is controlled to be sufficient to reduce formation ofdecomposition products to sufficiently low levels to provide containersand plates with suitable food contact compatible olfactory properties.Suitably 5 to 15 weight percent of the container comprises the basicinorganic compound, advantageously about 8 to 12 percent. When the basicorganic compounds are used, lower quantities are required, suitably fromabout 0.5 to 2.5 weight percent, advantageously 1.0 to 1.5 percent.Coupling agents and pigments may be utilized. Maleic anhydride andacrylic modified polypropylenes are suitable coupling agents for someembodiments.

[0071] The containers, bowls, trays and plates of this invention arepreferably produced by compounding a suitable resin/mineral composition;forming it into a sheet as shown in FIG. 1 and then thermoforming thesheet as shown in FIG. 2. These examples are illustrative and are notlimitative of a preferred commercial process which involves in-lineextrusion with regrind and thermoforming with multi-cavity mold beds.

[0072] Advantageously, the sheet is formed by an extrusion processutilizing a compounded polymer/mica basic inorganic compound or basicorganic compound mixtures. The final extrusion process renders a sheetwith excellent thermal properties, cut resistance, and food contactcompatible olfactory properties.

[0073] The aesthetically pleasing disposable microwaveable containers,trays, bowls and plates exhibit (a) food contact compatible olfactoryproperties, and (b) a melting point of at least 250° F. In addition, thecontainer or plate is dimensionally stable and resistant to grease,sugar, and water at temperatures of up to about 220° F. and are ofsufficient toughness to be resistant to cutting by serrated polystyreneflatware. The preferred mineral and basic inorganic compound or thebasic organic compound filled polypropylene plates, besides exhibitingfood contact compatible olfactory properties, exhibit on at least oneside a micronodular surface and a thickness uniformity characterized bya thickness coefficient of variation (COV) of less than about fivepercent.

[0074] Mica, a particularly preferred mineral filler, is a common namefor naturally occurring inert mineral of the phyllosilicate chemicalfamily, specifically potassium aluminosilicate whereby the aluminum ionsmay be partially replaced by iron and magnesium and part of thechemically bound water may be substituted by fluorine.

[0075] Mica is easily cleaved into thin, relatively regular, flexibleyet strong sheets (leaf-like flakes) with thickness in the range of halfa micron and aspect ratio as high as 300. Mica is much softer than otherinorganic fillers (wollastonite, glass) yet only slightly harder thantalc. Mica has a slippery tactile feel and low abrasiveness relative toother common inorganic fillers.

[0076] The reinforcement effect at 40 weight percent mica is equivalentto that of 30 weight percent glass fiber. Hard inorganic fibrous fillerssuch as glass (various lengths) and wollastonite (acicular structures)have drawbacks in some respects such as abrasiveness and are prone tofracture degradation during conventional melt processing. Other fibrous(organic) fillers are derived from wood and vegetable sources and arenot suitable for use in the manufacture of the containers of thisinvention since the organic fillers, when used in substantial amounts,tend to degrade during processing and they are also moisture sensitive.

[0077] In some applications it may be preferred to treat the mineraland/or basic inorganic compounds prior to using them in the inventivearticles. A suitable compound for this treatment is amnino-silane;sometimes referred to as a “coupling” agent.

[0078] Suitable basic inorganic and organic compounds used in theprocess include: calcium carbonate, sodium carbonate, sodium hydroxide,potassium carbonate, barium carbonate, aluminum oxide, sodium silicate,sodium borosilicate, magnesium oxide, strontium oxide, barium oxide,zeolites, sodium phosphate, potassium phosphate, magnesium phosphate,mixtures of silicon dioxide with one or more of the following oxides:magnesium oxide, calcium oxide, barium oxide, and mixtures of these orother basic inorganic or organic compounds such as sodium stearate,calcium stearate, potassium stearate, sodium citrate, potassium citrate,and mixtures of these basic compounds.

[0079] In the case where microwaveability is desired for a plasticdisposable food contact article, the not so perfect solution has beenthe use of relatively expensive high heat modified polystyrene based orheat resistant materials (e.g., unfilled PPO and SMA engineeringresins), where PPO refers to polyphenylene oxide and SMA refers tostyrene-maleic anhydride copolymer.

[0080] Mica or another mineral filler and the basic inorganic compoundor the basic organic compound filled polypropylene is compounded bypre-blending the polypropylene in pellet or flake form with mica powderand the basic inorganic compound or the basic organic compound powderand other additives (color concentrates, pigments, antioxidants,lubricants, nucleating agents, antistatic agents, etc.). This mixture isconveyed into the feed section addition point of a twin screwcompounding extruder, or compounded in a Banbury-type mixer to provide amelt-processed polyolefin composition. Alternatively, the components areadvantageously fed separately into the same or different points ofaddition, using combinations of volumetric and/or gravimetric (i.e.,loss in weight type) feeders as farther described herein.

[0081] For white pigmentation, titanium dioxide is preferred due tocombination of brightness, and opacity, as well as stability duringprocessing and final use. Surface treatment may be optionally used tofther enhance wetting, dispersion, compatibility with matrix resinswhereas the titanium dioxide forms may be of the rutile or anatase type.Alternate white pigments may also consist of calcined clay or blends ofcalcined clay with titanium dioxide. For black pigmentation, carbonblack is preferred due to a combination of desirable characteristicssuch as blackness, and dispersibility, the latter of which can becarefully controlled by choice of particle size and surface chemistry.Carbon black is amorphous carbon in finely divided form which is made byeither the incomplete combustion of natural gas (channel black) or byreduction of liquid hydrocarbons in refractory chambers (furnace black).

[0082] A twin screw extruder provides sufficient mixing action toeffectively cause the wetting and dispersion of the filler into thepolymer matrix. The twin screw extruder may be of the co-rotating orcounter-rotating type, where each type is equipped with different screwflight elements which are appropriate for the feed, mixing, and meltmetering zones. The discharge zone normally consists of a strand diewhere the exiting molten material strands are quenched in a circulatingwater bath followed by knife cutting into pellets. In a particularlypreferred embodiment, a Banbury-type mixer is used for compounding theresin, mica and basic compound as fiirer described herein.

[0083] Low molecular weight additives such as waxes, fluorinatedpolymers, and other specialty lubricants are suitably used as processaids to reduce the melt viscosity and improve throughput. Polyethleneresin may also be added to the blend. Other additives may includenucleating agents and antistatic agents. Antioxidants may be added insmall amounts, generally less than one weight percent, to minimize shearand thermal degradation of the polypropylene during the extrusion andforming processes as well as to promote the chemical stability of thesheet prior to and during final article use. Suitable antioxidants areadvantageously selected from the group of phenolics and phosphites andblends thereof. These are produced by Ciba-Geigy and General ElectricCorporation.

[0084] Plastic sheet extrusion equipment is suitable for the manufactureof multilayered or single layered mica or other mineral filler and thebasic inorganic or organic compound filled sheets of a polyolefinselected from the group consisting of polypropylene,polypropylene/polyethylene copolymer or blend, and mixtures of these.Melt strength of the sheets is improved when mica is used as a fillersince geometry of the mineral in the form of high aspect ratio flakesserves to provide “inter-particle connectivity” or physicalcross-linking. The food contact compatible olfactory properties areenhanced when in addition to the mica, basic inorganic compounds ororganic compounds such as calcium carbonate, sodium carbonate, potassiumcarbonate, barium carbonate, aluminum oxide, sodium silicate, sodiumborosilicate, magnesium oxide, strontium oxide, barium oxide, zeolites,sodium phosphate, potassium phosphate, magnesium phosphate, mixtures ofsilicon dioxide with one or more of the following oxides: magnesiumoxide, calcium oxide, barium oxide, and mixtures of these or other basicinorganic or organic compounds such as sodium stearate, calciumstearate, potassium stearate, sodium citrate, potassium citrate, andmixtures of these are mixed with mica or other mineral filler and thepolyolefin to produce the containers of this invention.

[0085] In FIG. 1 a process is shown for the manufacture of a singlelayer mineral filled polypropylene sheet or polypropylene filled withmineral and basic inorganic compounds or organic compounds set forthhereinabove. Previously compounded and pelletized mixtures ofpolypropylene, mineral filler and the basic inorganic compound ororganic compound, and other additives are gravity fed by a hopper 10into the feed zone of a single screw extruder system. Primary extruder11 has a 2 inch diameter screw with a {fraction (24/1)} length todiameter ratio. Optionally multilayer coextruded sheet can be producedby utilizing at least one additional single screw extruder 12,13,14 inconjunction with a combining feedblock with proper melt piping andmanifold arrangements. Suitably one to seven screw extruders areemployed, preferably three. A flexible lip flat sheet die 15 having awidth of 31 inches was used.

[0086] The sheet of this invention 16 enters the sheet takeoff portion(i.e., after the molten material exits the die) compromising athree-roll polishing/casting unit 17 with individually temperaturecontrolled rolls, a two-rubber roll sheet pull unit 18, and a dualturret, dual shaft winder, whereby only one shaft winder roll 19 may beused. The three takeoff units were mechanically tied together, were on acommon track, and can be automatically traversed from close die lipproximity to about 36 inch distant. During the extrusion process, thedistance between the die exit and the casting unit was maintained at 2inches. These three chrome rolls comprising the sheet casting unit areindividually temperature controlled by integral oil circulating pumpsand heat exchangers. Nip gaps are adjustable. A speed differentialbetween cast rolls and pull rolls is normally maintained such that pullroll speed is approximately within ten percent (10% ) of cast rollspeed. On a pilot line, achievable line speeds are in the range of1-12.5 feet per minute; while for a sheet on the order of 20 mil thick,the line speed is about 5-6 feet per minute. The sheet is wound on aroll 19. Table 1 shows the sheet process conditions employed for thesheet extrusion of mica and basic inorganic compound or the basicorganic compound filled polypropylene and the unfilled polypropylenecontrol. In a commercial operation, the speed is increased by a factorof 10 to 20 times.

[0087] Thermoforming is the pressing or squeezing of pliable materialinto final shape. In the simplest form, thermoforming is the draping ofa softened sheet over a shaped mold. In the more advanced form,thermoforming is the automatic, high speed positioning of a sheet havingan accurately controlled temperature into a pneumatically actuatedforming station whereby the article's shape is defined by the mold,followed by trimming and regrind collection.

[0088] Forming techniques other than conventional thermoforming are alsosuitable for the manufacture of articles described in the presentinvention. These include variations such as presoftening the extrudedsheet to temperatures below the final melting temperature, cutting flatregions (i.e., blanks) from the sheet, transfer of blanks by gravity ormechanical means into matched molds whereby the blanks are shaped intothe article by heat and pressure. The sheet from which the blanks havebeen cut out is collected as regrind and is recyclable. Conventionalpaperboard pressing equipment and corresponding forming tooling isoptionally modified to produce articles of this invention.

[0089] The extruded sheet used in a preferred thermoforming process asshown in FIG. 2 has a thickness of about 0.010 to 0.080 inches (10 to 80mils), suitably 0.010 to 0.050 inches. For the plates the preferredthickness is about 0.015 to 0.025 inches. Suitable filler loading levelin the extruded sheet is in the range of 10 to 50 weight percent, morepreferably 20-50 weight percent and most preferably 20-35 weightpercent. To achieve suitable food contact compatible olfactoryproperties, the basic inorganic compound loading level should be 5 to 15weight percent, advantageously 8 to 12 weight percent. For the basicorganic compound the loading levels should be 0.5 to 2.5 weight percent,preferably 1.0 to 1.5 weight percent. The mica flake aspect ratio in oneembodiment is in the range of 30-300, more preferably 15-250, withparticle size range of about 10-500 microns. The extruded sheetcomprises isotactic polypropylene homopolymer or polypropylenepolyethylene copolymer or blend or a mixture of these as base resin,preferably having a melt flow index in the range from about 0.3 to about4.0, more preferably 0.5-2.0 and most preferably about 1.5. Propylenecopolymers or blends with ethylene levels in the range of 1-10 molepercent, more preferably 2-5 mole percent, are optionally used. Thepreferred type of mica in some embodiments is muscovite, which is themost common form in commerce. Optionally other less common mica typessuch as phlogopite, biotite and fluorphlogopite are used. Although thereare an infinite number of compositions possible for these four generictypes due to isomorphous substitution which are mine specific, theselection of particular grades is driven by particle aspect ratio,particle size, price and availability.

[0090] Exemplary inorganic materials which may also be employed as aprimary mineral filler include talc, barium sulfate, calcium sulfate,magnesium sulfate, clays, glass, dolomite, alumina, ceramics, calciumcarbide, silica and so on. Many of these materials are enumerated in theEncyclopedia ofMaterials Science and Engineering, Vol. # 3, pp.1745-1759, MIT Press, Cambridge, MA (1986), the disclosure of which isincorporated herein by reference.

[0091] Mineral fillers are sometimes referred to by their chemicalnames. Kaolins, for example, are hydrous alumino silicates, whilefeldspar is an anhydrous alkali, alumino silicate. Bentonite is usuallyan aluminum silicate clay and talc is hydrated mangesium silicate.Glass, or fillers based on silicon dioxide may be natural or syntheticsilicas. Wollastonite is a calcium metasilicate whereas mica is apotassium alumino silicate. Mineral fillers are farther discussed below.

[0092] As noted above, clays may be employed as a primary filler. Thetwo most common of which are kaolin and bentonite. Kaolin refersgenerally to minerals including kaolinite which is a hydrated aluminumsilicate (Al₂₀₃.2SiO₂.2H₂O) and is the major clay mineral component inthe rock kaolin. Kaolin is also a group name for the minerals kaolinite,macrite, dickite and halloysite. Bentonite refers to hydrated sodium,calcium, iron, magnesium, and aluminum silicates known asmontmorillonites which are also sometimes referred to as smectites .

[0093] A large number of siliceous materials may also be employed as aprimary filler. These materials include diatomite, perlite, pumice,pyrophillite, silica, and talc. These minerals typically consist of analkali metal oxide or alkaline earth element oxide, and silicon dioxidetogether with a minor amount of water and other elements. Talc, forexample, includes from about 25% to about 35% MgO, 35-60% SiO₂ and about5% H₂O. These materials are farther described below.

[0094] Diatomite or kieselguhr is a sedimentary material formed bycenturies of life cycles of aquatic diatoms, a simple plant in the algaefamily with an opaline silica cell wall. Thousands of species of diatomshave flourished and continue to do so in both marine and lacustrineenvironments. Fossilized skeletal remains of diatoms in commercialquantities are found in many parts of the world.

[0095] Perlite is believed to result from hydration of volcanic glass orobsidian Generally, hydration is about 2-5% ; this water content isimportant to the expansibility of the perlite, influencing melting pointand supplying expansion steam.

[0096] The rapid expansion of dissolved gases in silica lavas duringvolcanic eruptions produces the light density pumice or pumicite. Thefiner pumicite particles are transported by wind away from the sourcevolcano, whereas pumice accumulates closer to the vent.

[0097] The hydrous aluminum silicate, pyrophilite, is formed byhydrothermal metomorphism of acid tuffs or braccias.

[0098] Silica sand is frequently obtained from the weathering ofquartz-containing act rock. Decomposition and disintegration of the rockwith decomposition of other minerals leaves a primary quartz sand thathas been concentrated by water movement. Induration of sands tosandstone results in another source for silica sand. Amorphous silica,or more properly cryptocrystalline or microcrystalline silica, is formedby the slow leaching of siliceous limestone or calcareous chert.

[0099] Talc is formed by the metamorphic (hydrothermal) alteration ofmagnesium silicates such as serpentine, pyroxene or dolomite.

[0100] The siliceous fillers are generally inert in most applications asshown by pH values in the range from about 6-10.

[0101] Sulfate minerals, such as gypsum and barite may likewise beemployed as a primary filler. Gypsum is the name given to the mineralthat consists of hydrous calcium sulfate (CaSO₄2H₂O), and also to thesedimentary rock that consist primarily of this mineral. In its purestate, gypsum contains 32.6% lime (CaO), 46.5% sulfur trioxide (SO₃),and 20.9% water. Single crystals and rock masses that approach thistheoretical purity are generally colorless to white, but in practice,the presence of impurities such as clay, dolomite, silica and ironimparts a gray brown, red or pink color to the rock.

[0102] There are three common varieties of gypsum: selenite, whichoccurs as transparent or translucent crystals or plates; satin spar,which occurs as thin veins (typically white) of fibrous gypsum crystals;and alabaster, which is compact, fine-grained gypsum that has a smooth,even-textured appearance. Most deposits or rock gypsum that are suitablefor industrial purposes are aggregates of fine to coarse gypsum crystalsthat have intergrown to produce a thick, massive sedimentary rock unitthat is 90-98% gypsum. Alabaster is highly prized because of itsuniformly fine particle size, but the more common deposits of rockgypsum consisting of coarser-grained selenite can generally be crushedand ground to produce a suitable filler and coating material.

[0103] Gypsum has a hardness of 2 on the Mohs scale, and can bescratched with the fingernail Large rock masses are easily crushed andground to a fine powder. The specific gravity of gypsum is about 2.31and the refractive index is about 1.53. Gypsum is slightly soluble inwater but it is an inert substance that resists chemical change. Theoil-absorption capacity of gypsum is fairly low (0.17-0.25 cm³g⁻¹).

[0104] Raw or crude gypsum is one of the forms used as fillers andcoatings, but for some purposes calcined or deadburned gypsum isdesired. In calcining, the gypsum is heated to abut 120-160° C. to driveoff free water and partially remove the water of crystallization. Thecalcined material or stucco, has a chemical composition of CaSO₄.½H₂O,and it readily takes up water. Calcination at higher temperatures(500-725° C.) results in a product called deadburned gypsum, which has acomposition of CaSO₄.

[0105] Anhydrite, a sulfate mineral and rock that is closely associatedwith gypsum in nature and has minor uses as a filler, in anhydrouscalcium sulfate (CaSO₄) containing 41.2% CsO and 58.8% SO₃. It istypically fine grained (like alabaster), and occurs in thick, massivesedimentary rock units. Anhydrite usually is white or bluish gray whenpure, but it may be discolored by impurities. Anhydrite has a hardnessof 3.5, a specific gravity of 2.98, and a refractive index of 1.57-1.61.

[0106] Thus, fillers commonly include:

[0107] Barium Salt

[0108] Barium Ferrite

[0109] Barium Sulfate

[0110] Carbon/Coke Powder

[0111] Calcium Fluoride

[0112] Calcium Sulfate

[0113] Carbon Black

[0114] Calcium Carbonate

[0115] Ceramic Powder

[0116] Chopped Glass

[0117] Clay

[0118] Continuous Glass

[0119] Glass Bead

[0120] Glass Fiber

[0121] Glass Fabric

[0122] Glass Flake

[0123] Glass Mat

[0124] Graphite Powder

[0125] Glass Spheres

[0126] Glass Tape

[0127] Milled Glass

[0128] Mica

[0129] Molybdenum Disulfide

[0130] Silica

[0131] Short Glass

[0132] Talc

[0133] Whisker

[0134] Particulate fillers, besides mica, commonly include:

[0135] Glass

[0136] Calcium carbonate

[0137] Alumina

[0138] Beryllium oxide

[0139] Magnesium carbonate

[0140] Titanium dioxide

[0141] Zinc oxide

[0142] Zirconia

[0143] Hydrated alumina

[0144] Antimony oxide

[0145] Silica

[0146] Silicates

[0147] Barium ferrite

[0148] Barium sulphate

[0149] Molybdenum disulphide

[0150] Silicon carbide

[0151] Potassium titanate

[0152] Clays

[0153] Whereas fibrous fillers are commonly:

[0154] Whiskers

[0155] Glass

[0156] Mineral wool

[0157] Calcium sulphate

[0158] Potassium titanate

[0159] Boron

[0160] Alumina

[0161] Sodium aluminum

[0162] Hydroxy carbonate

[0163] Suitably the extruded sheet includes coloring agents foraesthetic appeal, preferably titanium dioxide, carbon black, and otheropacifying agents in the range of 0.5-8 weight percent based on totalcomposition, preferably 1.5 to 6.5 weight percent. The extruded sheetcomprises minor amounts of other additives such as lubricants andantioxidants. These articles of manufacture may be suitably colored withpigments or dyes. Pigments are defined as small insoluble organic orinorganic particles dispersed in the resin medium to promote opacity ortranslucency. Usual pigments include carbon black, titanium dioxide,zinc oxide, iron oxides, and mixed metal oxides. Dyes are organic andsoluble in the plastic, and may be used alone or in combination withpigments to brighten up pigment based colors. All such colorants may beused in a variety of modes which include dry color, conventional colorconcentrates, liquid color and precolored resin.

[0164] The mineral filled polypropylene sheets are suitably formed intoplates, bowls, cups, trays, buckets, souffle dishes, and containersusing a forming or thermoforming process disclosed herein. In a pilotprocess, these articles of manufacture and containers may be made usingthe Comet Starlett thermoformer unit. This machine is capable of vacuumforming products from heat softened thermoplastic materials and isschematically depicted in FIG. 2. Sheet portions 23 having dimensions of17.5 inches by 16.25 inches were clamped on two opposing sides andinserted into an oven indicated at 22 equipped with upper 20 and lower21 heaters, whereby heater input settings were in the range of 20-30percent and hold times were on the order of 60-80 seconds. Under theseconditions, the oven air temperature as recorded by a digitalthermocouple was in the range of 221° F. to 225° F., while the sheetsurface temperature, as recorded by adhering indicator thermocouples,was approximately 330° F. to 340° F.

[0165] When the clamped and heat softened sheet 23 exits the oven 22, itmay be vacuum formed by either procedure (A) or (B) in a commercialprocess. Both methods utilize only one mold which is suitably fabricatedfrom epoxy thermoset materials or suitable mold materials includingaluminum, steel, beryllium, copper and the like. Mode (A) uses a malemold 24 whereby the sheet is sucked up to conform to it by means ofvacuum where the vacuum ports are present on the mold base as well as onthe periphery side of the container (i.e., flange area). Mode (B)arrangement is such that the vacuum direction is opposite to mode (A),where again vacuum holes are located around the base and periphery . Inthe case of mode (B), a female mold 25 is used, and this arrangement ispreferred since the air side of the sheet corresponds to the foodcontact side. In mode (B) the food contact side undergoes a beneficialtexturizing effect as a result of the heat treatment, whereby the resinflows around and outward from the mica particles close to the surfacecausing the mineral to become more exposed which creates a micronodularsurface as manifested by decreased gloss and increased surfaceroughness. The micronodular surface gives the container a stoneware orpottery-like appearance.

[0166] Advantageously, other thermoforming arrangements are suitable andmay be preferred in conventional sheet and web feed thermoformingcommercial production operations. Alternative arrangements include theuse of drape, vacuum, pressure, free blowing, matched die, billow drape,vacuum snap-back, billow vacuum, plug assist vacuum, plug assistpressure, pressure reverse draw with plug assist vacuum, reverse drawwith plug assist, pressure bubble immersion, trapped sheet, slip,diaphragm, twin-sheet cut sheet, twin-sheet rolifed forming or anysuitable combinations of the above. Details are provided in J. L.Throne's book, Thermoforming, published in 1987 by Coulthard. Pages 21through 29 of that book are incorporated herein by reference. Suitablealternate arrangements also include a pillow forming technique whichcreates a positive air pressure between two heat softened sheets toinflate them against a clamped male/female mold system to produce ahollow product. Metal molds are etched with patterns ranging from fineto coarse in order to simulate a natural or grain like texturized look.Suitably formed articles are trimmed in line with a cutting die andregrind is optionally reused since the material is thermoplastic innature. Other arrangements for productivity enhancements include thesimultaneous forming of multiple articles with multiple dies in order tomaximize throughput and minimize scrap.

[0167] Various measurements used herein include melt flow index, SSIrigidity (sometimes referred to below as simply “rigidity”), ParkerRoughness and so forth. Unless otherwise indicated explicitly or bycontext, these terms have the meaning set forth below.

[0168] The melt flow rate (MFR) or melt index is a common and simplemethod for determining the flow properties of molten polymers. (As usedherein, ASTM D 1238-95, Condition 230/2.16). Resin is introduced andmelted in a cylindrical space. After temperature equilibration isreached, a weight is used to push a plunger vertically downward wherebythe resin is extruded through a narrow orifice. The usual testtemperature and the temperature utilized herein for polypropylene is230° C. and the load is 2.16 Kg. Extruded material is collected andweighed and the time required to extrude a specific weight is recorded.MFR or melt index is expressed as grams per minutes, or grams per 10minutes, which is the weight of material extruded in a 10 minute timeperiod. MFR is inversely proportional to both polymer viscosity andpolymer molecular weight.

[0169] SSI rigidity is measured with the Single Service Institute PlateRigidity Tester originally available through Single Service Institute,1025 Connecticut Ave., NW. Washington, D.C. The SS1 Rigidity testapparatus has been manufactured and sold through Sherwood Tool, Inc.,Kensington, Conn. This test is designed to measure the rigidity (i.e.resistance to buckling and bending) of paper and plastic plates, bowls,dishes, and trays by measuring the force required to deflect the rim ofthese products a distance of 0.5 inch while the product is supported atits geometric center. Specifically, the plate specimen is restrained byan adjustable bar on one side and is center fulcrum supported. The rimor flange side opposite to the restrained side is subjected to 0.5 inchdeflection by means of a motorized cam assembly equipped with a loadcell, and the force (grams) is recorded. SSI rigidity is expressed asgrams per 0.5 inch deflection. A higher SSI value is desirable sincethis indicates a more rigid product. All measurements were done at roomtemperature and geometric mean averages for the machine and crossmachine direction are reported.

[0170] The Parker Roughness method was used to determine roughness usingthe Messmer Parker Print-Surf Roughness. Operation procedure details arereferenced in the Messmer Instruments Ltd. User manual for theinstrument (Model No. ME-90) which is distributed by Huygen Corporation.The flat specimen is clamped under I Mpa pressure against a narrowannular surface by a soft backing and the resistance of air flow of thegap between the specimen and the annulus is measured. The air flow isproportional to the cube of the gap width and the roughness is expressedas the root mean cube gap in units of micrometers. Higher Parkerroughness values indicate higher degrees of surface roughness.

[0171] Gloss is reported as “gloss units at 75 or 60 degrees.” Glossmeasurements were conducted following TAPPI Standard Method T-480-OM 92.

[0172] The following examples are illustrative of the present invention.It should be understood that the examples are not intended to limit theinvention and that various modifications may be made by those skilled inthe art without changing the essential characteristics of the invention.

EXAMPLES 1-8

[0173] Mica filled polypropylene sheets (20 mil) and unfilledpolypropylene sheets (22 mil) were extruded, as shown and described inconnection with in FIG. 1, with conditions specified in Table 1. Theseextrusion process conditions may be varied as necessary to producesheets which are of acceptable quality. Specifically, the operabletemperature ranges for barrel zones 1,2, and 3 are about respectively,350 to 425° F., and 450 to 500° F. the adaptor, feedblock, and dietemperatures can all be in about the range of 450 to 500° F. the rangeof values for extruder drive amperes, extruder speed, melt pressure, diepressure, chill roll temperature, and line speed are about respectively,12 to 20 amp., 60 to 100 RPM, 1500 to 2500 psi, 450 to 650 psi, 120 to140° F., and 3 to 8 FPM. Sheets are subsequently vacuum thermoformedinto plates and other containers and lids as set forth in FIGS. 14through 33. There is reported in Tables 2 and 3, respectively, rigidityvalues and caliper data for the sidewall, bottom, and flange (rim) areasof vacuum formed plates using condition (B) of FIG. 2 and having adiameter of 10.25 inches. In each table, individual rigidity values areshown for each specimen. In addition, the caliper uniformity forsidewall, bottom, and flange areas are reported for each specimen, alongwith the summary statistics. Specifically, the caliper of each platespecimen in Tables 2 and 3 was measured ten times using a Fowler gaugefor each of the three regions of interest consisting of the sidewall,bottom, and flange areas, and the average value for each plate specimenis reported along with the corresponding standard deviation in thousandsof inches or mils (i.e., individual plate statistics). In the case ofthe three plates of Table 2, the caliper summary statistics (expressedin the average properties row) were obtained on the basis of averaging30 measurements, wherein the standard deviation is reported for each ofthe three regions of interest. In the case of the five plates of Table3, the caliper summary statistics were calculated on the basis ofaveraging 50 measurements where again the standard deviation is reportedfor each of the three regions of interest. Therefore, the caliper dataof Tables 2 and 3 located in the average property rows pertain to globalstatistics rather than individual plate statistics. The caliperuniformity parameter consists of the coefficient of variation (COV)which is calculated as the standard deviation of caliper divided by themean caliper, whereas the ratio is multiplied by 100, whereas the abovedescribed global averages and associated standard deviations areemployed. A lower COV value is desirable since it signifies improvedcaliper uniformity for mica filled polypropylene plates with respect tounfilled polypropylene plates. Tables 2 and 3 show that mica reduces COVof polypropylene from 9.9 to 4.3 in sidewall and from 9.6 to 2.0 in theflange area. Therefore, caliper uniformity in sidewall improved by morethan a factor of 2 and caliper uniformity in the flange improved by overa factor of 4. The improvement of caliper uniformity is critical forpromoting plate dimensional stability during food transport andmicrowave cooking operations. In great contrast to mica filledpolypropylene plates, the unfilled polypropylene plates exhibited poorquality as evidenced by poorly defined rim area, and sharkskin, veryrough surface. These data demonstrate that mica greatly improves thedrawability of polypropylene as evidenced by improved caliperuniformity, as well as improved thermoformability, both of which are dueto enhanced melt strength relative to unfilled polypropylene. Mica isthe preferred reinforcing mineral filler for enhancing the melt strengthbecause of its highly regular, high aspect ratio morphology which can bethought of as resulting in “inter-particle connectivity” or “physicalcross-linking”. The significant reinforcing effect of mica is alsoevidenced by a SSI plate rigidity value of 671 grams per 0.5 inches forPP/mica at a basis weight of about 350 lbs. per square foot ream versus342 grams per 0.5 inches for unfilled PP at a basis weight of about 280lbs. per 3000 square foot ream. TABLE 1 Sheet Extrusion Conditions forMica Filled Polypropylene and Unfilled Polypropylene CONDITION PP/MICAUNFILLED PP Barrel Zone 1 (° F.) 395 395 Barrel Zone 2 (° F.) 425 425Barrel Zone 3 (° F.) 475 475 Adaptor (° F.) 470 450 Feed block (° F.)470 460 Die Zones 1-3 (° F.) 470 475 Extruder RPM 80 70 Drive amperes 1619 Melt pressure (psi) 1700 1780 Die pressure (psi) 550 825 Line speed(FPM) 6.1 5.0 Chill roll temp. (° F.) 130 137

[0174] TABLE 2 Caliper and Rigidity Data for 10-1/4 Inch PlatesThermoformed From Unfilled Polypropylene Sheet Plate Specimen RigiditySidewall Bottom Caliper Flange Example (g/0.5 in.) Caliper (mil) (mil)Caliper (mil) 1 364 18.7 ± 1.9 20.7 ± 0.8 22.9 ± 2.8 COV* 10.1 3.9  12.22 382 19.2 ± 20. 20.6 ± 0.4 23.3 ± 0.8 COV 10.4 1.9   3.4 3 280 19.6 ±1.9 20.6 ± 0.5 23.3 ± 2.8 COV  9.7 2.4  12.0 Average 342 ± 54.4 19.19 ±1.89 20.64 ± 0.58 23.15 ± 2.21 Properties COV  9.85 2.81  9.55

[0175] TABLE 3 Caliper and Rigidity Data for 10-1/4 inch PlatesThermoformed From Polypropylene/Mica/TiO₂ sheet Plate Bottom FlangeSpecimen Rigidity Sidewall Caliper Caliper Example (g/0.5 in.) Caliper(mil) (mil) (mil) 4 705 18.3 ± 1.1 17.4 ± .05 18.2 ± 1.0 COV* 6.0 2.95.5 5 659 17.0 ± 1.5 17.9 ± 0.7 18.4 ± 0.5 COV 8.8 3.9 2.7 6 654 17.3 ±1.6 17.0 ± 0.6 18.2 ± 0.7 COV 9.2 3.5 3.8 7 669 16.9 ± 1.2 16.7 ± 1.118.9 ± 0.8 COV 7.1 6.6 4.2 8 668 16.3 ± 1.0 16.3 ± 0.9 19.0 ± 0.9 COV6.1 5.5 4.7 Average 671 ± 20  17.3 ± 0.76 17.1 ± 0.6  18.5 ± 0.38Properties COV 4.3 3.5 2.0

EXAMPLES 9-11

[0176] Thirty percent mica and ten percent calcium carbonate filledpolypropylene sheet was run on a commercial extrusion line. The extruderwas a 6″ Egan single screw with an EDI flex lip die. In these Examples9-11, the resulting melt temperature was approximately 400° F. and thetemperature for Barrel Zones 1-5 were approximately 400/396, 390/390,370/370, 370/370, and 370/371 as shown in Table 4.

[0177] Lower melt temperatures are typically preferred. Process melttemperatures of 370° F. or so will help control undesirable odors in theproduct. Process melt temperature as used throughout refers to ameasured value of the temperature of a composition when thepolypropylene is molten and unless otherwise stated, is indicative ofthe maximum temperature of a particular step.

[0178] For the runs reported in Table 4, an auger feeder was installedjust above the feed throat of the extruder to introduce colorconcentrates for producing green, blue, and eggshell colored sheet. Theconcentrate was added at levels between 1% -5% . TABLE 4 ExtrusionConditions for 30% Mica/10% Calcium Carbonate Filled PolypropyleneSet/Actual Conditions Green Blue Eggshell Barrel Zone 1 Temp (F.)400/396 400/398 400/399 Barrel Zone 2 Temp (F.) 390/390 390/390 390/391Barrel Zone 3 Temp (F.) 370/370 370/370 370/370 Barrel Zone 4 Temp (F.)370/370 370/370 370/370 Barrel Zone 5 Temp (F.) 370/371 370/370 370/370Adaptor Temp (F.) 370 370 370 Melt Temp (F.) 400 400-405 404/405 DieZone 1 Temp (F.) 380 385 385 Die Zone 2 Temp (F.) 370 370 370 Die Zone 3Temp (F.) 370 370 370 Die Zone 4 Temp (F.) 370 370 370 Die Zone 5 Temp(F.) 380 385 385 Screw RPM 30 30 30 Drive Amperes 325-345 335-352347-350 Screen Pack 20 mesh 20 mesh 20 mesh Back Pressure (psi)2350-2510 2370-2600 2515-2680 Line Speed (fpm) 30/28/20 30/28/2227/26/20 Throughput (lb./hr.) 725 725 725 Top Stack Roll Temp 120-130120-130 120-130 (F.) Middle Stack Roll Temp 120-130 120-130 120-130 (F.)Bottom Stack Roll 120-130 120-130 120-130 Temp (F.) Roll Gap-top (mil)17 17 17 Roll Gap-bottom (mil) 23 23 23 Nip Roll Pressure 50 80 80 DieGap (mil) 15 middle-30 15 middle-30 15 middle-30 edges edges edgesDie-Full Width (in) 52 52 52 Die to Nip Distance (in) Approximately 4.5Approximately 4.5 Approximately 4.5 Sheet Width (in) 51.5 51.5 51.5Sheet Caliper (mil) 17.5/18.5/24 17.5/18.5/24 17.5/18/24 Color AugerSetting (%) 4 4 1 Trim Regrind Used Yes Yes No Footage Produced 1200011000 15000

EXAMPLES 12-17

[0179] Aroma Profile Test Method

[0180] The Sensory Analysis Center at Kansas State University hasdeveloped a profiling protocol in which a highly trained panelidentifies specific odors and rates their intensity. The intensity scaleis a 15-point “universal” scale of the type typically chosen for sensorystudies, where 1 is barely perceptible or threshold and 15 is extremelystrong. If an attribute or odor component is not listed in the tableswhich follow, it means it is not present and would score a 0. The panelmembers are selected on the basis of a series of screening tests thatinclude basic taste, odor recognition, taste intensity recognition,taste intensity ranking, and a personal interview to evaluateavailability and personality traits. Training, which includes thefundamental sensory principles and all aspects of the profile technique,is done over a 4-12 month period.

[0181] The panelists work as a group to arrive at a description of theproduct.

[0182] Individual results are compiled by the panel leader anddiscussion follows in which disagreements are discussed until aconsensus is reached on each component of the profile. Referencematerials and more than one session usually are required in order toreach the consensus.

[0183] The procedure for resin is to place 40 ml. of resin in a 340 ml.glass brandy snifter, which is covered with a watch glass. Sheet samplesare cut into two 2″× 2″ sections and placed in the same size brandysnifter. In testing, panelists found that some samples had initial odorcomponents that disappeared rapidly. Therefore an initial impact and asustained impact were evaluated for each sanple. The initial impact wasjudged immediately after the watch glass had been removed; the sustainedimpact was judged 10 seconds after the watch glass had been removed.Typical results are shown in the Table 5 below for Low Odor and HighOdor Compositions. “Low” odor formulations were produced using lowermelt processing temperatures in compounding and adding 10% calciumcarbonate to the formulation. The sheets were prepared as shown anddescribed in connection with Examples 1 through 11. TABLE 5 High Odorvs. Low Odor Polypropylene Composites: Effect of Adding 10% CaCO₃ ODORPROFILE FOR COMPOUNDED RESIN Consensus Odor Profile on Resin ResinImpact (Kansas State University Sensory Analysis Center) Resin InitialSustained Petroleum Pungent Musty Scorched Medicinal Sweet Waxy SoapyHigh 9.0 3.5 8.0 4.0 7.0 3.5 3.0 Odor Low 5.5 2.5 2.5 4.5 1.5 2.0 4.5Odor High Odor Resin Low Odor Resin 65.63% Polypropylene 55.63%Polypropylene 30% Mica 30% Mica 2.5% Coupling Agent 10% CaCO₃ 1.87%Pigment 2.5% Coupling Agent 1.87% Pigment

[0184] High Odor and Low Odor compositions were compounded utilizing theprocess melt temperatures indicated in the first column of Table 6 andformed into sheets as described above. Thermoformed sheet was evaluatedfor aroma profile. TABLE 6 ODOR PROFILE FOR SHEET FORMED FROM COMPOUNDEDRESIN AT TWO TEMPERATURES Sheet Impact +HC,14 +UZ,14/32 Consensus OdorProfile on Sheet Resin Initial Sustained Petroleum Pungent MustyScorched Medicinal Sweet Waxy Soapy High Odor 12.0 6.0 10.0 8.0 7.5 4.54.0 370° F. High Odor 11.0 8.0 7.5 7.5 6.0 3.5 2.0 459° F. Low Odor 5.52.0 3.5 4.0 2.0 2.5 2.5 371° F. Low Odor 5.5 2.0 3.0 3.5 2.0 3.5 46° F.

[0185] The foregoing data demonstrates that: when a basic moietycontaining compound was added to the mica polyolefin composition, aresin was produced having suitable food contact compatible olfactoryproperties. Significant decreases in the initial and sustained odorswere observed and the scorched, pungent, and petroleum aroma componentswere removed or greatly reduced and these undesirable components seem tobe replaced with sweet, waxy, and soapy aroma components.

[0186] When compounded pellets are subjected to sheet extrusion, thosewithout calcium carbonate increase in the disagreeable components(pungent and petroleum) and increase in the initial and sustained odoroutput with subsequent processing. In contrast, when pellets containcalcium carbonate, no increase in undesirable aroma components wasobserved and no increase in the initial or sustained odor was producedwith subsequent processing. Test panel data correlated well withanalytical techniques as can be seen from the discussion and exampleswhich follow.

[0187] C8/C9 Ketones

[0188] The precise nature of the odor causing compounds inpolypropylene/mica compositions is not known; however, it has been foundthat undesirable odors correlate well with eight carbon (C8) and ninecarbon (C9) alkyl ketones as described hereinafter, and may beassociated with such compounds.

[0189] A Likens-Nickerson stearnmethylene chloride extraction techniquewas used to extract possible odor causing compounds frompolypropylene/mica compositions and produce a concentrate. Theextraction was performed until complete. The concentrate was analyzedthrough gas chromatography/mass spectrometry to produce chromatogramssuch as those shown in FIGS. 3 and 4. The abscissa is an arbitrary timescale, while the ordinate is an arbitrary abundance scale. The peak foralkyl C8 (labeled as A) ketone assigned to be 4-methyl-2-heptanone,appears on both FIGS. 3 and 4 at slightly above 16.8 on the time scaleas indicated; while the peak for C9 alkyl ketone (labeled as B),assigned to be 4,6-dimethyl-2-heptanone appears slightly below 17.6 onthe time scale in both chromatograms. Other peaks of interest on FIGS. 3and 4 are C7 ketones at slightly above 15.1, 15.6 and 16.3 on theabscissa. The peaks are respectively assigned to be 2-heptanone,3-heptanone and 4-heptanone. They are respectively labeled as C, D andE. There is also shown on both FIGS. 3 and 4 peaks for what are to beassigned to be various C7 alcohols at about 18, 18.2 and 18.8 on theabscissa. These compounds are respectively labeled as F, G and H on thediagrams and are assigned to be 2-heptanol, 3-heptanol, and 4-heptanol.The C8/C7 ratios referred to hereinafter are ratios of the abundance atthe peaks assigned to be 4-methyl-2-heptanone to the abundance at thepeak assigned to be 4-heptanone as measured by Likens-Nickersonextraction followed by gas chromtography/mass spectrometry. That is, theC8/C7 ratio for a given sample is the ratio of peak intensity (height)of peak A to the peak intensity of peak E. Similarly, the C9/C7 ratio isthe ratio of the peak intensity of peak B to the peak intensity of peakE in FIGS. 3 and 4 for a given sample.

[0190]FIG. 3 is a chromatogram characteristic of extracted material fromextruded pellets having a relatively strong odor wherein the C8 and C9ketones indicated each have an extractable concentration of about 10parts per million parts by weight in the product. FIG. 4 is achromatogram characteristic of extract from relatively “low odor”extruded pellets substantially free of C8 and C9 ketones as shown.Generally, “low odor” compositions reduce concentration of C8 and C9ketones over “high odor” compositions by 2/3 with 1/5 being typical and1/10 being preferred. Thus, in general, melt-compounded compositions inaccordance with the invention have extractable concentrations of C8 andC9 alkyl ketones of less than about 3.5 ppm (weight) with less than 2ppm being typical and less than 1 ppm being particularly preferred.

[0191] It can also be seen from the chromatograms in FIGS. 3 and 4 thatthe adjacent C7 ketone levels are comparable in both the “low odor” and“high odor” compositions. Thus, the C8/C7 ratio can be used as analternative indicator of desirable olfactory characteristics. Typically,“low odor” compositions in accordance with the invention have a C8/C7ratio at least five times less than high odor compositions with at leastten times less being typical.

[0192] In preferred compositions according to the invention, C8/C7ratios as measured by Likens-Nickerson extraction followed by gaschomatography/mass spectrometry are generally less than about 0.5 or soas is seen from in the examples which follow. C8/C7 ratios of less thanabout 0.3 are typical and C8/C7 ratios of less than about 0.1 areparticularly preferred. The articles of the invention and the pelletsfrom which they are made are further characterized by an odor indexwhich is determined by commercially available equipment in accordancewith the procedure detailed below.

[0193] Odor Index

[0194] Melt processed compositions produced in accordance with thepresent invention, particularly extruded pellets from which articlessuch as plates and bowls are made, characteristically exhibit relativelylow odor as opposed to conventionally formulated mineral/polypropylenecompositions. Generally the odor index (as defined herein) is less thanabout 0.75, with less than or equal to about 0.6 being preferred. Ingeneral, the lower the odor index, the lower the odor intensity of themineral filled/polypropylene pellets. Less than or equal to about 0.5 ismost preferred with a practical lower limit believed to be somewherearound 0.1 or so. Thus, in accordance with the invention, meltcompositions will generally have an odor index of less than about 0.75and typically from about 0.60 to about 0.1.

[0195] The odor index of a particular melt-processed composition isreadily determined using conventional materials and equipment.

[0196] The odor index is defined as the arithmetic average of all sensorintegrals for a given mineral-filled polypropylene sample including botha primary mineral filler and calcium carbonate or other odor suppressingcompound divided by the arithmetic average of all integrals for a filledpolypropylene sample including a primary mineral filler, but no odorsuppressing basic compound, or in equation form:${{Odor}\quad {Index}} = \frac{\begin{matrix}{{Average}\quad {readings}\quad {of}\quad {pellets}\quad {including}\quad a\quad {primary}} \\{{mineral}\quad {filler}\quad {and}\quad {calcium}\quad {carbonate}\quad {or}\quad {other}} \\{{odor}\quad {suppressing}\quad {compound}}\end{matrix}}{\begin{matrix}{{average}\quad {readings}\quad {of}\quad {pellets}\quad {including}\quad {mineral}} \\{{filler}\quad {only}\quad {without}\quad {an}\quad {odor}\quad {suppressing}\quad {basic}} \\{compound}\end{matrix}}$

[0197] A commercially available “electronic nose” aroma scanning deviceis used. Typically, such devices utilize a plurality of conductivitysensors to determine the odor of a sample. The particular device used inthe discussion which follows uses 32 sensors whose response isintegrated over time. The various integrals are averaged for each sampleand the single value is used in the numerator and the denominator of theabove equation.

[0198] A sample of the present invention is described in Table 7 andfollowing. TABLE 7 Index Numerator Composition Amount (Wt. ComponentManufacturer Product Number Percent) Polypropylene Exxon Escorene 477255.63 Mica Franklin L-140 30.0 Industrial Minerals, Inc. Calcium HuberQ-325 10.0 Carbonate Coupling Agent Aristech Unite NP-620 2.5 TitaniumTioxide TR-23 1.87 Dioxide

[0199] The above components were extruded on a 90 mm BerstorffCo-Rotating Twin Screw Extruder with underwater pelletizing under thefollowing conditions:

[0200] 200 rpm screw speed

[0201] with the following set temperature profile:

[0202] Zone 1-510° F.

[0203] Zone 2-485° F.

[0204] Zone 3-400° F.

[0205] Zone 4-380° F.

[0206] Zone 5-380° F.

[0207] Zone 6-380° F.

[0208] Head Flange -425° F.

[0209] Screen Changer -425° F.

[0210] Die -440° F.

[0211] Throughput appx. 900 LB/HR to produce pellets, the odor values ofwhich are used in the numerator of the above equation.

[0212] The preferred instrument to perform the aroma intensitymeasurements is an AromaScan® modelA32 (AromaScan, Hollis, N.H., USA).This instrument employs a dynamic head space type of measurement, inwhich nitrogen gas flows through a sample vial and carries aromavolatiles to the sensors. All pellet samples are analyzed in triplicatewith the final results averaged to minimize measurement noise. In theillustrations which follow, The “Acquisition Parameters” method of theinstrument is set with a sampling interval of 1 and a detectionthreshold of 0.2. The “Multisampler-SP” method of the instrument setsthe platen temperature (100° C. for the examples herein). Two othertemperatures (115° C. and 125° C.) are automatically set. TheMultisampler-SP method is also used to set the parameters in Table 8 tomeasure aroma intensity. TABLE 8 AromaScan ® Setting Sample EquilibriumTime: 5 minutes Vial Size: 22 ml Mix Time: 0 Mix Power: 1 RelativeHumidity: 10% Sampling Time: 4 minutes Wash Time: 5 minutes DataCollection Time (minutes): 19 Time Between Injections 20 (minutes):

[0213] In the recognition window, start and end are set at 1. Inaddition to the foregoing, the “Vial Pressurization Control” is set at20 kPa, the “Vial Needle Flow” is set at 50 ml/min nitrogen; “TransferLine Flow” across the sensors, between, before and after samples is setat 150 ml/min. All gas flows are for dry nitrogen.

[0214] A response of each of the 32 sensors of the AromaScan® machine isintegrated over a time interval of 55-150 seconds. The initial 55seconds is allowed to let humidity/moisture exit the system to a greatextent before integration is started. The 150 second integration endtime was chosen to allow the sensor signals to return to baseline, atwhich time all significant signal has been integrated. The varioussignals seen after 150 seconds are insignificant in terms of the odormeasurement, as can be seen from FIG. 5. FIG. 5 is a plot of sensorresponse vs. time for each of the 32 sensors of the AromaScan® device,where individual responses are shown as various lines on the diagram.

[0215] Using the foregoing procedure and composition, 2.0 grams ofcompounded polymer pellets are weighed and placed in the 22 ml, crimptop, septum capped vials and analyzed automatically by the instrument. Adenominator, or reference sample is prepared as described in connectionwith Tables 7 and 8, except that no calcium carbonate is used; i.e. thesample has 65.63% polypropylene.

[0216] There is shown in FIG. 6 the results for various extrudedpolypropylene/mica pellets. The data points shown on FIG. 6 are actuallythe response integrals for a particular sensor. The abscissa on FIG. 6indicates each of the 32 elements; while the ordinate is thetime-integrated response of the corresponding element in arbitraryunits. There is shown as curve A the (integrated) sensor responses forthe numerator sample prepared as above. This sample has an odor index of0.625. There is also shown a denominator sample prepared in accordancewith the numerator sample procedure except that polypropylene wassubstituted for calcium carbonate at curve B as in the “high odor”compositions of the Kansas State Trials discussed above in connectionwith Examples 12-17. As can be seen, this composition has an odor indexof 1.0 by definition. There is also shown on FIG. 6 a third curve (C)representative of more preferred compositions prepared in accordancewith the present invention. Curve C represents a composition prepared inaccordance with Examples 28 through 30 below (Table 11) wherein the odorindex is about 0.4375 which means its response integrals are on average0.4375 times those of the sample reference or “high odor” of curve B.

[0217] Through the use of an automated instrument, the odor intensity ofthe melt-compounded pelletized composition can be reduced to a singlevalue. While the foregoing sets forth a particular and preferred methodof determining the odor intensity index, it may also be possible toemploy other instruments consistent with this protocol since suchinstruments are readily available. If such alternative instrument isemployed the standard composition detailed above should be used toensure that calibration is proper. As noted, the reference ordenominator composition is prepared by substituting polypropylene forthe calcium carbonate (or-other basic compound) of the numeratorcomposition.

EXAMPLES 18-26

[0218] A series of resin compositions and sheet products were preparedin accordance with the discussion above and characterized by C8/C7ketone ratio and odor panel testing. Variables included calciumcarbonate addition, process atmosphere (air or nitrogen) and processmelt temperature. Results appear in Table 9 for examples 18 through 26.TABLE 9 CaCO₃ Effect of Process Conditions and Compositions on Odor ofPP/Mica Composites Odor Panel Data Type “Scorched” (Banbury or ProcessC₈/C₇ Sustained Odor Profile Extruded Atmosphere CaCO₂ Process MeltKetone (Total Component Example Sheet) (Air/N₂) (Yes/No) TemperatureRatio Intensity) Intensity 18 Brabender Air Yes 370° F. 0.055 2.0 0Banbury Compounded 19 Brabender Air Yes 460° F. 0.6 4.0 5.0 BanburyCompounded 20 Sheet N₂ Yes 460° F. 0.3 21 Brabender Air Yes 460° F. 0.64.0 5.0 Banbury Compounded 22 Sheet Air Yes 370° F. 0.15 2.0 0 23 SheetAir No 370° F. 1.3 6.0 4.5 24 Sheet Air Yes 400° F. — 5.0 2.5 25 SheetAir No 460° F. 0.9 8.0 26 Sheet Air Yes 460° F. 0.7 2.0 0

[0219] The resins of Examples 18, 19, and 21 were prepared on aBrabender device (C.W. Brabender, model EPL2V5502) with a Banbury mixhead (model R.E.E.6, 230v, 11a) with a mixing time of 5-10 minutes.

[0220] The sheet samples, Examples 20 and 22 through 26, were preparedfrom precompounded resin pellets extruded under the conditions shown inTable 10. TABLE 10 Sheet Extrusion Conditions for PP/Mica Pilot ExtruderCONDITIONS ACTUAL SET POINT Barrel Zone 1 (° F.) 354-378 360-375 BarrelZone 2 (° F.) 366-410 370-410 Barrel Zone 3 (° F.) 371-460 370-460Adapter temp (° F.) 359-460 370-460 Feed Block Temp (° F.) 370-468370-460 Die Zones 1-3 temps 368-462 370-460 (° F.) Extruder RPM 110 110Drive Amperes 15-23 — Melt Pressure (psi) 1050-1850 — Die Pressure (psi)745-910 — Line Speed (FPM) 8.25-9.74 — Chill roll temp. (° F.) 130 —

[0221] The odor of PP/mica composites (pellets or sheet) is affected bytemperature, atmosphere, and by the addition of a basic filler such asCaCO₃. The C8/C7 ketone ratio is consistent with the odor panel data andshows that offensive odor components decrease with:

[0222] Using lower processing temperatures

[0223] Using a base such as CaCO₃ as a buffering agent

[0224] Processing under inert atmosphere such as N₂.

EXAMPLES 27-30

[0225] Particularly preferred, low odor compositions are prepared by wayof a sequential process in a Banbury mixer at relatively lowtemperatures. A typical Banbury apparatus is shown schematically in FIG.7. An apparatus 110 includes generally a feed hopper 112 provided with afeed ram 114 coupled to a weight cylinder 116 which may be varieddepending on the force required for a particular process. Feed hopper112 has a lower portion 118 which communicates with a mixing chamber 120provided with a pair of rotors 122, 124. The material is supplied tohopper 112 through a charging door indicated at 126, and/or fed througha feed port located at 128. Chamber 120 is further provided with adischarge door 130 which is positioned above a conveyor indicated at132. Such apparatus is well known for compounding thermoplasticcompositions.

[0226] A conventional non-sequential process is operated as follows: (a)discharge door 130 is closed; (b) ram 114 is drawn up; (c) theingredients are added; (d) the ram is lowered and the rotors activated;(e) mixing is complete when a combination of temperature and work hasbeen achieved (power draw on mixer motor falls off); (f) at which pointthe discharge door is opened and the batch is gravimetrically suppliedto a conveyor; and finally (g) the batch is conveyed to a single screwextruder and pelletized. The apparatus melts the polymer through sheargenerated by the rotors and walls against the components being mixed.One may rely on shear (that is, mechanical work) to soften thethermoplastic components or apply some auxiliary heat directly either inthe feed hopper or the chamber through the use of heating coils,infrared devices, steam jacketing and the like , or, alternatively,preheating the polymer externally prior to feeding.

[0227] It has been found that melt compositions prepared in a sequentialBanbury process exhibit superior stiffness as measured by flexuralmodulus properties and low odor. In a sequential process in accordancewith the invention, two feed steps are used in order to minimize thetime heated or molten polypropylene is in contact with the mica or othermineral filler as will be explained in connection with FIGS. 7 and 8.

[0228] In a first, melt mix step, door 130 is closed and ram 114 isdrawn up. Polypropylene, polyethylene, titanium dioxide, other pigmentsand the like are added. Ram 114 is lowered and the rotors 122, 124 arerotated to shear the material. A typical power curve (at constant rotorspeed) for amperage supplied to the mixing motors for the inventivesequential process is shown in FIG. 8, a plot of amperage versus time inhours:minutes:seconds.

[0229] When the pair of rotating rotors are first started in the meltmix step, the current draw is indicated at point P1 on FIG. 8 where itcan be seen power applied to the polymer is quite high. The current drawreaches a maximum at about P2 where the polymer begins to softenrapidly. At P3 after a minute or two the current draw is at a minimumwhile the components are being mixed when the polymer is in a softenedstate. Mica and calcium carbonate may then be added simultaneously in amineral filler addition step as will be detailed below.

[0230] After the polymer is softened, ram 114 is again drawn up and themica and calcium carbonate may be added at the time corresponding to P4on the diagram. The material may be added through a door 126 or feedport 128. The current draw at constant rotor speed again increases asshown at P5 and eventually begins to decay as shown at P6 and P7. Morepreferred is to add the mica and calcium carbonate mixture at about thetime corresponding to P2 prior to complete softening of the resin.Alternatively, polypropylene may be externally preheated to about 240°F. or so (along with the mixing chamber to the same temperature) and allof the ingredients are simultaneously added for maximizing processthroughput. Preferred drop batch temperature at the end of Banbury meltcompounding, that is, maximum melt processing temperature for this stepis up to about 425 degrees Fahrenheit. At the time corresponding to P7,the door may be opened and the batch of material (a batch size is about200 pounds) conveyed to an extruder to be pelletized. TABLE 11Comparison of Compounding Processes Compound Flexural Odor Index;COMPOUNDING Modulus 9″ Plate Approximate PROCESS (Tangent), PSI Rigidity(g/0.5″) (Compound) Twin Screw 718,000 417 0.625 Example 27 Banbury591,000 378 0.375 (no-sequential) Example 28 Banbury 708,000 416 0.41(sequential, 1 min. pre-heat) Example 29 Banbury 635,000 352 0.3875(Sequential, 2 min. premelt) Example 30

[0231] Table 11 shows compound flexural modulus (as measured by ASTMmethod D 790-95a), corresponding plate rigidity, and aroma intensityindex on four indicated compounding processes designated as Examples27-30. In the case of twin-screw (Example 27), high modulus is obtainedbut with higher odor with relatively low throughput, in the range of 900lb/hr, which is less than half the output of Banbury compoundingprocesses (utilizing a Stewart-Boiling Banbury Mixer with batch sized inthe range of 150-200 lb) listed herein. In the case of non-sequentialBanbury process, low modulus is obtained with corresponding low platerigidity with lower odor and high throughput. In the last two casescorresponding to sequential Banbury processes designated as “1 min.pre-heat” and “2 min. pre-melt”, the short 1 minute preheat case(Example 29) is preferred because it gives high compound modulus andhigh plate rigidity (comparable to twin screw case) with benefits ofboth low odor and high throughput, in excess of 2000 lb/hr.

[0232] The twin screw formulation in the above table contains PP/30%mica/10% CaCO3 with 2.5% coupling agent (maleic anhydride modified PPgrade Aristech Unite NP-620) and no polyethylene. The formulationcorresponding to all three listed Banbury processes in above tablecontain PP/30% mica/10% CaCO3/0.5% TiO2/4% LLDPE with no coupling agentwhere such ingredients have the following sources and grades: MicaFranklin Minerals L-140, CaCO₃=Huber Q325, PP= Exxon Escorene PP4772,LLDPE=Novapol Novachemical G1-2024A.

[0233] The Banbury “non-sequential” case (Example 28) in Table 11corresponds to adding all ingredients together with a total compoundingtime of about 4.5 minutes followed by conversion of the batch (havingtemperature of 430° F.) to pellets using a continuous 10″ single screwextruder equipped with one 30 mesh and one 20 mesh screen, and anunderwater pelletizing die assembly, with a pelletizing temperature inthe range of 455-470° F.

[0234] The Banbury “sequential 2 min premelt” case (Example 30) in Table11 corresponds to a 2 minute period for melting the PP/LLDPE mixture (inthe presence of CaCO₃ and TiO₂) to a maximum temperature of about 350°F., followed by adding mica and thereafter mixing for a period of about105 sec to achieve a batch temperature of about 430° F., followed byconversion to pellets with a pelletizing temperature of about 460° F.The Banbury “sequential, 1 min pre-heat” case (Example 29) in Table 11corresponds to about a 1 minute period for presoftening the PP/PEmixture (in the presence of TiO₂, or alternatively adding the TiO₂ withthe mica and calcium carbonate) to a maximum temperature of about 260°F., followed by adding the mica/CaCO₃ mixture and thereafter mixing toachieve a batch temperature of about 425° F., followed by conversion topellets with a pelletizing temperature of about 425° F. In thispreferred mode, it has been found that polymer preheating aids inpreserving compound stiffness (required for rigid articles ofmanufacture) and intimate contact of mica with odor suppressing agent(CaCO₃) aids the production of low odor material.

[0235] Pellets from the above mentioned Banbury compounding processeswere subsequently extruded at 370° F. as cast sheets in the range of17-18 mil. Sheet line conditions also included a screw RPM value of 100,a chill roll temperature of about 130° F., drive amperage value of about22, melt pressure of about 2000 psi, die pressure of about 970 psi, anda line speed of about 7 ft/min. Plates were subsequently vacuumthermoformed using a female mold and trimmed and tested for rigidity.

EXAMPLES 31-41

[0236] Extruded mica filled polypropylene sheets prepared as describedin Examples 1 through 8 were characterized with respect to surface glossand roughness. Table 12 shows 75 degree gloss and Parker Roughness(airflow method) data for an extruded mica filled polypropylene sheetversus same properties for the food contact (air) side of vacuum formed10.25 inch plates produced according to condition (B) of FIG. 2 usingthe same sheet formulation. The unique thermally induced micronodularsurface is characterized by significant decrease in gloss andsignificant increase in roughness as shown in the two photomicrographsin FIGS. 9A and 9B, which results in a stoneware or pottery likeappearance with aesthetic appeal. (The Parker Roughness method isdescribed above). The upper photomicrograph of FIG. 9A is of athermoformned plate surface, while the lower photomicrograph of FIG. 9Bis of sheet.

[0237] The photomicrographs of FIGS. 9A and 9B were obtained from a10×15 mm piece cut out of a plate bottom. The sheet sample was mountedwith surface of interest up on a specimen stub, and coated withgold/palladium. The stub was placed in a JEOL 840A Scanning ElectronMicroscope (SEM). Photomicrographs of the samples were taken at 75×magnification, 30 degree tilt, 39 mm working distance at 3 kv. TABLE 12GLOSS AND ROUGHNESS PROPERTIES OF THE FOOD CONTACT SIDE OFPOLYPROPYLENE/MICA/TIO₂ PLATE SURFACE VERSUS NEAT EXTRUDED SHEET GLOSSPARKER ROUGHNESS EXAMPLE (75 DEGREES) * (MICRONS) 31 (Plate) 22.4 13.4132 (Plate) 30.6 14.05 33 (Plate) 24.8 14.89 34 (Plate) 24.3 14.24 35(Plate) 24.5 12.48 PLATE AVERAGE 25.3 ± 3.1 13.8 ± 0.9 36 (Sheet) 45.7 5.92 37 (Sheet) 47.2  7.43 38 (Sheet) —  5.89 39 (Sheet) —  6.35 40(Sheet) —  5.84 41 (Sheet) —  8.15 SHEET AVERAGE 46.5  6.6 ± 0.97

[0238] As shown in Table 12, the food contact side is rougher asevidenced by increased roughness and decreased gloss relative to theneat extruded sheet. The rough appearance is desirable for purpose ofcreating the micronodular surface giving the container and plate astoneware or pottery-like look.

EXAMPLES 42-43

[0239] Mica filled polypropylene sheets were successfilly vacuumthermoformed into 12 oz. oval microwave containers, whereby the base wasproduced using mode (B) of FIG. 2 and the lid was produced using mode(A) of FIG. 2. In contrast, attempts to form unfilled polypropylenesheet into the same container were not successfull.

EXAMPLES 44-46

[0240] Sheet rolls (17.5 wide), at three calipers were extruded asdescribed in Examples 1 through 8 in connection with FIG. 1. Table 13summarizes the PP/40% mica material and process conditions. Table 14summarizes the PP/40% mica sheet properties. TABLE 13 PP/Mica ExtrusionProcess Conditions Summary Barrel Barrel Barrel Die Chill Zone 1 Zone 2Zone 3 Adapter Feed Die Zone 3 Roll Temp. Temp. Temp. Temp. Block DieZone 2 Temp. Screw Temp. Plate (F.) (F.) (F.) (F.) Temp. Line Zone 1Temp.(F.) (F.) RPM Melt Die (F.) Size Actual/ Actual/ Actual/ Actual/Actual/ Speed Temp.(F.) Actual/ Actual/ Actual/ Drive Pressure PressureActual/ (in.) Set Set Set Set Set (fpm) Actual/Set Set Set Set Amperes(psi) (psi) Set 11 395/395 452/425 475/475 470/470 470/470 9.27 470/470469/470 470/470 125 18.3 1387 694 130/130 10 376/375 410/410 431/430430/430 430/430 8.32 430/430 430/430 430/430 130 19.3 2012 737 130/130 9 375/376 410/410 434/430 430/430 430/430 8.07 430/430 430/430 430/430132 24.2 2112 686 130/130

[0241] TABLE 14 PP/Mica Sheet Property Summary Plate Size Overall BasisWeight-Avg. (in.) Overall Caliper-Avg. (mil) (lb./3000 ft.{circumflexover ( )}2) 11 18.46 ± 0.36 308.07 ± 13.72 10 17.20 ± 0.10 288.80 ±9.89   9 16.94 ± 0.10 268.11 ± 7.50 

EXAMPLE 47-49

[0242] Plates from sheet specifications set forth in Examples 31-41 wereproduced using 1-up water cooled female molds (with pressure box/vacuumassembly), followed by matched metal punch trimming. Mold temperaturewas 70° F., while sheet temperatures for the 9, 10, and 11 inch plateruns were respectively 300° F., 310° F., and 295° F. The 9 and 10 inchplates were produced at 20 cycles/minute while the bulk of the 11 inchplates were made at 25 cycles/minute.

[0243] Oven temperature control on the commercial machine was good dueto the combination of top quartz heaters and bottom calrod heaters withproper zoning. In general, higher temperatures produce moremicronodularity at the expense of more pronounced sheet sag andwrinkling while low temperatures tend to reduce sag at the expense ofdiminished stoneware or pottery-like appearance.

[0244] Best results (i.e., micronodular matte eating surface without“webbing” or wrinkling) were obtained by increasing the top oventemperature by 3-5° F. and decreasing the bottom by a correspondingamount. This ability to selectively control oven temperature in effectfacilitated determination of the preferred process temperature window ofPP/mica sheets.

EXAMPLE 50-54

[0245] Sheets and plates were prepared as illustrated in Examples 1through 8 and FIGS. 1 and 2. Table 15 shows sheet extrusion and formingconditions. FIGS. 10 and 11 respectively, show gloss and plate rigidityversus mica level (at constant mica/TiO₂ ratio). TABLE 15Extrusion/Forming Conditions Barrel Zone 1 375° F. Barrel Zone 2 410° F.Barrel Zone 3 430° F. Adaptor 430° F. Feedblock 430° F. Die Zones 1/2/3430° F. RPM 130 Chill Roll 130° F. Target Sheet Caliper 18.3 mil SheetWidth 18.0 inches Comet Former Top Heater 20% Comet Former Bottom Heater35% Comet Former Time 50-60 seconds Plate Diameter 11 inch

EXAMPLES 55-62

[0246] Commercial sheet extrusion runs of several mica filledpolypropylene formulations were conducted. These sheets suitably have abasis weight of about 200 to 950, per 3000 square foot ream, preferablyabout 200 to 400 per 3000 square foot ream. These mica filledpolypropylene sheets had a mica content in the range of 25 to 35 weightpercent.

[0247] The extrusion of coupled mica and polypropylene blends wasconducted on a 6″ commercial extruder line. The extruder was an Egan{fraction (24/1)} L/D with a general purpose screw. The die was anExtrusion Die Inc. 52″ coat hanger type. The stack conditioning rollswere top polished chrome, middle matte (40 RA surface), and bottompolished chrome. The matte chill roll assisted with the formation of themicronodular surface during thermoforming of the sheet with beneficiallyimproving breadth of forming temperature window in contrast withnon-matted smooth sheets. The differences between surfaces of thevarious sheets and plates made therefrom may be better appreciated byreference to FIGS. 12 and 13 hereof FIG. 12A is a scanning electronphotomicrograph of surface A of Table 16, while FIG. 12B is a scanningelectron photomicrograph of surface B of Table 16. FIG. 13A is ascanning electron photomicrograph of surface G of Table 16 and FIG. 13Bis a scanning electron photomicrograph of surface H of Table 16. TABLE16 Roughness and Gloss Properties of PP/30% Mica Extruded Sheets andThermoformed Plates Sheet Thermoforming Temperature Parker RoughnessSurface (° F.) (microns) Gloss (75%) A —  8.56 ± 0.39 4.99 ± 0.11 B —15.82 ± 0.74 8.05 ± 0.30 C 305 13.14 ± 0.74 14.3 ± 1.0  D 300 11.74 ±0.86 11.6 ± 1.0  E 292 12.10 ± 0.82 11.7 ± 1.0  F 265 10.63 ± 0.68 8.20± 0.6  G — 6.17 82.10 H — 5.14 80.75

[0248] For a non-matte extruded sheet, usually plate gloss and plateroughness are inversely related (e.g., high gloss corresponds to lowroughness and vice versa as demonstrated in prior art data generallyobtained). In that case, achieving desirable micronodular texture iswithin a temperature range (about 295° F. to 305° F.) where above thisrange the forming process is sag limited while below this range theplate exhibits poor micronodular character as manifested by high glossand low roughness.

[0249] The use of a matte roll in the chill roll stack portion of theextrusion process effectively broadens the commercially attractivethermoforming process temperature range (about 265° F. to 305° F.).Specifically, plates having acceptable surface micronodularity can beformed at lower temperatures, whereby the decrease in plate roughness iscompensated by an unexpected decrease in plate gloss using sheet surface(A). This beneficial increase in plate forming temperature window fromabout 10° F. to about 40° F. is brought about by imparting a mattesurface finish to the extruded sheet.

[0250] The extruded sheet used in the suitable forming and thermoformingprocess, or the preferred thermoforming process as shown in FIG. 2 has athickness of about 0.010 to 0.080 inches, suitably 0.010 to 0.030inches, and preferably 0.015 to 0.25 inches. Suitable mica fillerloading level in the extruded sheet is in the range of 25-30 weightpercent, whereby mica flake aspect ratio is in the range of 30-300, morepreferably 80-120, with particle size range of about 50-500 microns.

[0251] By matte finishing one side of the sheet using matte roll, thecommercial thermoforming was suitably conducted at a broader temperaturewindow of about 265° F. to 305° F. while without matte finishing, thethermoforming using the same commercial equipment was conducted at atemperature of about 295° F. to 305° F.

[0252] The runs on commercial equipment using PP/30% mica and PP/25%mica formulations showed that the thermoforming temperature window rangehas been expanded from about 10° F. (previous trial) to as high as about35° F. This is primarily due to the fact that we beneficially used amatte roll in the chill roll stack during the extrusion process. Thisgave a smooth matte finish for the air side of the sheet (i.e., plateeating surface) while the rougher bottom side was in contact with thesandblasted mold side during the formning process. Use of matte sheet,in turn, enabled forming at lower temperatures (which is good for sagavoidance) without much loss in micronodularity. Specifically, theforming window was in the range of 265° F. to about 300° F. to 305° F.where best balance of process stability and product appearance/texturewas seen at about 280° F. to 290° F.

[0253] Preferred Articles

[0254] The sheet of the present invention is suitably formed into platesor bowls having a circular configuration. These articles of manufacturemay also be square or rectangular in shape having angular corners, suchas found in a tray. Further, additional shapes such as triangular,multi-sided, polyhexal, etc., are contemplated including compartmentedtrays and plates as well as oval platters. In each contemplatedembodiment, all corners are rounded or curved with a preferred pluralityof embodiments of the present invention being depicted in FIGS. 14through 33. The various embodiments shown in FIGS. 14 through 33, whileillustrative of the present invention, are not intended to limit theinvention and those of skill in the art may make changes withoutchanging the essential characteristics of the invention. Thesecontainers may also have other features such as ridges, emboss, anddeboss patterns suitable for enhancing the properties of the containersof this invention. These container's bottom sections may have a convexcrown to improve stability and reduce rocking during use.

[0255] Throughout the following description, each of the dimensions arereferenced with respect to a given diameter D which, in accordance withthe present invention as illustrated in FIGS. 14 through 17 isapproximately 8.75 inches. However, the particular diameter of thecontainer is not a critical limitation and is only set forth herein byway of example. It is the relationship between the various portions ofthe rim configuration which are essential.

[0256] The planar inner region in accordance with the illustratedembodiment of a plate in FIGS. 14 through 17 has a radius X1 which isequal to approximately 0.3 D -0.4 D and preferably 0.348 D. This plateis descibed generally in U.S. Pat. No. 5,326,020 the disclosure of whichis incorporated herein by reference. Adjoining an outer periphery of theplanar inner region 150 is a sidewall portion 152 including annularregion 154 having a radius of curvature equal to approximately 0.05D-0.06 D and preferably 0.0572 D with the center point thereof beingpositioned a distance Y1 from the planar inner region 150. Includedangle 156 of the annular region 154 is from about 40° to about 700 andpreferably about 60°-65° or approximately 62°. Adjoining the peripheryof the annular region 154 is the first frusto-conical region 158 whichslopes upwardly at an angle A1 with respect to the vertical from about20° to about 35° and preferably about 25°-30° or approximately 27.50.Additionally, the frusto-conical region 158 is adjacent to the arcuateannular region 160 which includes a radius of curvature in the range of0.015 D to 0.03 D and preferably approximately 0.024 D with the centerpoint thereof being positioned a distance Y2 from the planar innerregion 150. The included angle 162 of the arcuate annular region 160 mayrange from about 61° to about 82° and is preferably 66° to 77° or about73°. The second portion 164 of the arcuate annular region 160, that isthe distal portion of the arcuate annular region 160, is positioned suchthat a line tangent to the curvature of the arcuate annular region 160at the second portion 164 slopes downwardly and outwardly at an angle ofapproximately 0° to 12°.

[0257] The combination of the annular region 154 and arcuate annularregion 160 should combine to position the second portion 164 of thearcuate annular region 160 in the manner set forth herein above. Thatis, the included angle 156 of the annular region 154 when combined withthe included angle 162 of the arcuate annular region 160 with the firstfrusto-conical region 158 spanning therebetween, positions the secondportion 164 of the arcuate annular region 160 in a manner such that asecond frusto-conical region 166, which extends substantiallytangentially from the distal end of the second portion 164 of thearcuate annular region 160 extends outwardly and doWnwardly at an angleof about 0° to 12°. The second frustro-conical region 166 is of a lengthin a range from about 0.03 D to about 0.05 D and is preferably 0.04 D.Because the second frusto-conical region 166 extends substantiallytangentially from the second portion 164 of the arcuate annular region160, the second frusto-conical region 166 extends outwardly anddownwardly at an angle A3 in the range from approximately 0° to 12° withrespect to a horizontal plane formed by the planar inner region 150.

[0258] Adjoining an outer periphery of the second frusto-conical region166 is the lip 168 which is in the form of yet another frusto-conicalregion which extends outwardly and downwardly from the secondfrusto-conical region 166. The lip 168 is of a length of at least 0.005D and is preferably approximately 0.010 D. Further, the lip (168)extends at an angle A2 of no more than 45° from vertical, preferablyapproximately 15° to 30° with respect to the vertical plane.

[0259] At the transition between the second frusto-conical region 166and the lip 168 is a transition region 170. The transition region 170includes a radius of curvature R3 which is in the range of about 0.008 Dand 0.01 D and is preferably approximately 0.0092 D with the centerpoint thereof being positioned a distance Y3 from the planar innerregion 150. Additionally, the transition region 170 has an includedangle A4 of approximately 48° to 70°.

[0260] The plates disclosed in FIGS. 18 through 20 generally have thedimensions of the plates disclosed in U.S. Pat. No. 5,088,640 which isincorporated herein by reference in its entirety. These containers mayhave other features such as ridges, emboss, and deboss patterns suitablefor enhancing the properties of the containers of this invention. Thereis shown in FIGS. 18 through 20 a plate having a planar center includingan outer peripheral surface. The planar center forms a bottom for theplate. An outwardly projecting sidewall includes a first rim portionjoined to the outer peripheral surface of the planar center and a secondrim portion joined to the first rim portion. The first and second rimportions form a sidewall of the plate. A third rim portion is joined tothe second rim portion of the outwardly projecting sidewall and a fourthrim portion is provided for forming an outer edge of the container. Thefirst rim portion is joined to the peripheral surface of the planarcenter at an angle having a second predetermined radius. The third rimportion is joined to the second rim portion at an angle having a thirdpredetermined radius. The fourth rim portion is joined to the third rimportion at an angle having a fourth predetermined radius. The four radiias well as the four included angles are selected for enhancing rigidityof the plate as compared to a container made from the same material byother means as is further described below.

[0261] Illustrated in FIGS. 18 through 20, there is a plate 180 whichincludes a planar center 182 which, in turn, includes an outerperipheral surface 184. This center region 182 may have a slight convexcrown to improve plate stability during use. The planar center 182 formsa bottom for the plate 180. An outwardly projecting sidewall 186includes a first rim portion 188 which is joined to the outer peripheralsurface 184 of the planar center 182. A second rim portion 190 is joinedto the first rim portion 188. The first rim portion 188 and the secondrim portion 190 form the outwardly projecting sidewall 186 which formsthe sidewall of the plate 180. A rim 192 includes a third rim portion194 which is joined to the second rim portion 190 of the outwardlyprojecting sidewall 186. A fourth rim portion 196 is joined to the thirdrim portion 194. The fourth rim portion 196 forms the outer edge of theplate 180.

[0262]FIG. 20 illustrates a partial cross-sectional view of a plate,diameter D, according to the present invention. The plate 180 defines acenter line 204. A base or bottom-forming portion 200 extends from thecenter line 204 to an outer peripheral surface 202.

[0263] From the center line 204 a predetermined distance X12 extendstoward the outer peripheral surface forming portion 202. A distance Y12extends a predetermined distance from the base or bottom-forming portion200 upwardly therefrom. A radius R12 extends from the intersection pointof the distance X12 and Y12 to form a first rim portion 206 of theoutwardly projecting sidewall 205. The farst rim portion 206 is defmedby an arc A12 which extends from the vertical line defined at the outerperipheral surface 202 to a fixed point 210. The arc A12 may beapproximately 60°.

[0264] A distance X22 extends from the center line 204 to apredetermined point. A distance Y22 extends from the base orbottom-forming portion 200 of the plate 180 downwardly a predetermineddistance. A radius R22 extends from the intersection of the lines X22and Y22 to form a second rim portion 208 of the sidewall 205. The radiusR22 extends from the first fixed point 210 to the second fixed point 212through an arc A22. The arc A22 may be approximately 4°.

[0265] A distance X32 extends from the center line 204 to apredeterminded distance. A distance Y32 extends from the base orbottom-forming section 200 of the plate 180 to project upwardly apredetermined distance. A radius R32 extends from the intersection ofthe lines X32 and Y32 to form the third rim portion 214 of the rim 216.The radius R32 extends from the second fixed point 212 to a third fixedpoint 218. An arc A32 is formed between the second fixed point 212 andthe third fixed point 218 to extend a predetermined distance. The arcA32 may be approximately 55°.

[0266] A distance X42 extends a predeterminded distance from the centerline 204. Similarly, a distance Y42 extends from the base orbottom-forming section 200 of the plate 180 to project upwardly. Aradius R42 extends from the intersection of the lines X42 and Y42 toform a fourth rim portion 217 of the rim 216. An arc A42 is formedbetween the third fixed point 218 and a fourth fixed point 220 atdiameter D from the center line. The arc A42 may be approximately 60°. Asection 220 forms the outer edge of the plate.

[0267] The container made according to the present invention may haveany particular size as desired by the user so long as the relativeprofile dimensions are maintained. More specifically, ovals, rectangleswith rounded corners and other shapes may be made having this profile.In various embodiments of the present invention the container may be a9-inch or 11-inch plate with profile coordinates as illustrated in FIGS.18 through 20 having the dimensions, angles, or relative dimensionsenumerated in Tables 17 through 19. TABLE 17 Dimensions and Angles For9″ Plate DIMENSION and ANGLES VALUE (inches or degrees) R12 0.537 X123.156 Y12 0.537 R22 2.057 X22 5.402 Y22 0.760 R32 0.564 X32 4.167 Y320.079 R42 0.385 X42 4.167 Y42 0.258 A12 60.00° A22 4.19° A32 55.81° A4260.00° D 9.00 BOTTOM CONVEX CROWN 0.06

[0268] TABLE 18 Dimensions and Angles For 11″ PLATE DIMENSION/ANGLESVALUE (inches or degrees) R12 0.656 X12 3.857 Y12 0.656 R22 2.514 X226.602 Y22 0.929 R32 0.689 X32 5.093 Y32 0.097 R42 0.470 X42 5.093 Y420.315 A12 60.00° A22 4.19° A32 55.81° A42 60.00° D 11.00 BOTTOM CONVEXCROWN 0.06

[0269] TABLE 19 Dimensions For 9 and 11 INCH PLATE DIMENSION RATIO ORVALUES (Dimensionless or degrees) ANGLE PREFERRED MINIMUM MAXIMUM R12/D0.060 0.045 0.075 X12/D 0.351 0.280 0.420 Y12/D 0.060 0.045 0.075 R22/D0.228 0.180 0.275 X22/D 0.600 0.480 0.720 Y22/D 0.084 0.065 0.100 R32/D0.063 0.050 0.075 X32/D 0.463 0.370 0.555 Y32/D 0.009 0.007 0.011 R42/D0.043 0.034 0.052 X42/D 0.463 0.370 0.555 Y42/D 0.029 0.023 0.035 A1260.00° 55.00° 75.00° A22 4.19° 1.00° 10.00° A32 55.81° 45.00° 75.00° A4260.00° 45.00° 75.00°

[0270] Salient features of the plate illustrated in FIGS. 18 through 20generally include a substantially planar center portion (which may becrowned as noted above and illustrated throughout the various figures)with four adjacent rim portions extending outwardly therefrom, each rimportion defining a radius of curvature as set forth above and furthernoted below. The first rim portion 10 extends outwardly from the planarcenter portion and is convex upwardly as shown. There is defined by theplate a first arc A12 with a first radius of curvature R12 wherein thearc has a length S1. A second rim portion is joined to the first rimportion and is downwardly convex, subtending a second arc A22, with aradius of curvature R22 and a length S2. A third, downwardly convex, rimportion is joined to the second rim portion and subtends an arc A32.There is defined a third radius of curvature R32 and a third arc lengthS3. A tangent to the third arc at the upper portion thereof issubstantially parallel to the planer center portion as shown in FIG. 20.A fourth rim portion is joined to the third rim portion, which is alsodownwardly convex. The fourth rim portion subtends a fourth arc A42 witha length S4, with a radius of curvature R42.

[0271] The length of the second arc, S2 is generally less the length ofthe fourth arc S4, which, in turn, is less than the length S1 of thefirst arc A12. The radius of curvature R42 of the fourth arc is lessthan the radius of curvature R32 of the third rim portion, which inturn, is less than radius of curvature R22 of the second rim portion.The angle of the first arc, A12 is generally greater that about 55degrees, while, the angle of the third arc, A32 is generally greaterthan about 45 degrees as is set forth in the foregoing tables. The angleof the fourth arc A42 is generally less than about 75 degrees and morepreferably is about 60 degrees.

[0272] Typically, the length S1 of arc A12 is equivalent to the lengthS3 of arc A32 and R12 of the first rim portion is equivalent in lengthto the radius of curvature R32 of the third rim portion.

[0273] Generally speaking, the height of the center of curvature of thefirst arc (that is the origin of ray R12) above the central planarportion is substantially less than, perhaps twenty five percent or soless than, the distance that the center of curvature of the second rimportion (the origin of ray R22) is below the central planar portion. Inother words, the length Y12 is about 0.75 times or less the length Y22.

[0274] So also, the horizontal displacement of the center of curvatureof the second rim portion from the center of curvature of the first rimportion is at least about twice the length of the first radius ofcurvature R12. The height of the center of curvature of the third rimportion above the central planar portion is generally less than theheight of the center of curvature of the fourth rim portion above theplane of the central planar portion. The horizontal displacement of thecenter of curvature of the second rim portion is generally outwardlydisposed from the center of curvature of the third and fourth rimportions.

[0275] A final noteworthy feature of the plate of FIGS. 18 through 20 isthat the height of the center of curvature of the third rim portionabove the planar central portion is less than about 0.75 times theradius of curvature R42 of the fourth rim portion; while the height ofthe center of curvature of the fourth rim portion above the plane of thecentral portion is at least about 0.4 times the first radius ofcurvature R12.

[0276] Yet other embodiments of this invention include trays which haveeither the DIXIE® Superstrong profile as illustrated in FIGS. 21 through24 and/or described in U.S. Pat. No. 5,326,020 assigned to the assigneeof the present invention and incorporated herein by reference into thisapplication. These trays may have other features such as ridges, emboss,and deboss patterns suitable for enhancing the properties of the traysof this invention. Throughout the following description of FIGS. 21through 24, each of the dimensions are referenced to either the lengthD1 or the width D2, which are approximately 10.90 and 8.00 inchesrespectively. D1 is larger than or equal to D2. However, the particularlength and width of these containers is not a critical limitation and isonly set forth herein by way of example. It is the relationship betweenthe various portions of the rim configurations which are essential. Theplanar inner region 101 in accordance with the illustrated embodiment inFIGS. 21A through 24, has a length IX which is equal to approximately0.3 D1 to 0.4 D1 and 0.3 D2 to 0.4 D2 and preferably 0.354 D1 andpreferably 0.342 D2. Adjoining an outer periphery of the planar innerregion 230 is a sidewall portion 232 including annular region 234 havinga radius of curvature equal to approximately 0.02 D1 to 0.03 D1 and0.025 D2 to 0.035 D2 and preferably 0.023 D1 and 0.031 D2 with thecenter point thereof being positioned a distance Y1 from the planarinner region 230. Included angle 236 of the annular region 234 is fromabout 40° to about 80° and preferably about 65° to 75° or approximately69°. Adjoining the periphery of the annular region 234 is the firstfrusto-conical region 238 which slopes upwardly at an angle Al withrespect to the vertical from about 10° to about 50° and preferably about15° to 25° or approximately 210. Additionally, the frusto-conical region238 is of a length greater than about 0.05 D1 and 0.055 D2, preferablyfrom about 0.1 D1 to 0.2 D1 and 0.15 D2 to 0.25 D2 and more preferablyapproximately 0.15 D1 and 0.19 D2. Further, adjoining the firstfrusto-conical region 238 is the arcuate annular region 240 whichincludes a radius of curvature in the range of 0.005 D1 to 0.007 D1 and0.007 D2 to 0.009 D2 and preferably approximately 0.006 D1 and 0.008 D2with the center point thereof being positioned a distance Y2 from theplanar inner region 230. The included angle 242 of the arcuate annularregion 240 may range from about 40° to about 92° and is preferably 65°to 87°. The second portion 244 of the arcuate annular region 240, thatis the distal portion of the arcuate annular region 240 is positionedsuch that a line tangent to the curvature of the arcuate annular region240 at the second portion 244 slopes downwardly and outwardly at anangle of approximately 0° to 12°.

[0277] The combination of the annular region 234 and arcuate annularregion 240 should combine to position the second portion 244 of thearcuate annular region 240 in the manner set forth herein above. Thatis, the included angle 246 of the annular region 234 when combined withthe included angle 242 of the arcuate annular region 240 with the firstfrusto-conical region 248 spanning therebetween, positions the secondportion 244 of the arcuate annular region 240 in a manner such that thesecond frusto-conical region 250, which extends substantiallytangentially from the distal end of the second portion 244 of thearcuate annular region 240 extends outwardly and downwardly at an angleof about 0° to 12°. The second frusto-conical region 250 is of a lengthin a range from about 0.045 D1 to about 0.055 D1 and 0.030 D2 to about0.040 D2 and is preferably 0.052 D1 and 0.034 D2. Because the secondfrusto-conical region 250 extends substantially tangentially from thesecond portion 244 of the arcuate annular region 240, the secondfrusto-conical 250 extends outwardly and downwardly at an angle A3 inthe range from approximately 0° to 12° with respect to a horizontalplane formed by the planar inner region 230.

[0278] Adjoining an outer periphery of the second frusto-conical region238 is the lip 252 which is in the form of yet another frusto-conicalregion which extends outwardly and downwardly from the secondfrusto-conical region 250. The lip 252 is of a length of at least 0.006D1 and 0.009 D2 and is preferably approximately 0.010 D1 and 0.013 D2.Further, the lip 252 extends at an angle A2 of no more than 45° fromvertical, preferably approximately 10 to 30° with respect to thevertical plane and more preferably approximately 20°.

[0279] At the transition between the second frusto-conical region 250and the lip 252 is a transition region 254. The transition region 254includes a radius of curvature R3 which is in the range of about 0.005D1 to 0.007 D1 and 0.007 D2 to 0.009 D2 and is preferably approximately0.006 D1 and 0.008 D2 with the center point thereof being positioned adistance Y3 from the planar inner region 230. Additionally, thetransition region 254 has an included angle A4 of approximately 48° to80°.

[0280] There is shown in FIGS. 25 through 28 still yet anotherembodiment of the inventive articles. Throughout the followingdescription of FIGS. 25 through 28, each of the dimensions arereferenced with respect to a given diameter D which, in accordance withthe present invention as illustrated in FIGS. 25 through 28, isapproximately 7.5 inches. However, the particular diameter of thecontainers is not a critical limitation and is only set forth herein byway of example. It is the relationship between the various portions ofthe rim configuration which are essential. The planar inner region 260in accordance with the illustrated embodiment in FIGS. 25 through 28,has a radius X1 which is equal to approximately 0.2 D to 0.3 D andpreferably 0.25 D. Adjoining an outer periphery of the planar innerregion 260 is a sidewall portion 262 including annular region 264 havinga radius of curvature equal to approximately 0.05 D to 0.15 D andpreferably 0.11 D with the center point thereof being positioned adistance Y1 from the planar inner region 260. Included angle 266 of theannular region 264 is from about 45° to about 75° and preferably about60° to 70° or approximately 65°. Adjoining the periphery of the annularregion 264 is the first frusto-conical region 268 which slopes upwardlyat an angle A1 with respect to the vertical from about 15° to about 45°and preferably about 20° to 30° or approximately 25°. Additionally, thefrusto-conical region 268 is of a length greater than about 0.1 Dpreferably from about 0.17 D to about 0.19 D and more preferablyapproximately 0.18 D. Further, adjoining the first frustro-conical isthe arcuate annular region 270 which includes a radius of curvature inthe range of 0.015 D to 0.030 D and preferably approximately 0.023 Dwith the center point thereof being positioned a distance Y2 from theplanar inner region 260. The included angle 272 of the arcuate annularregion 270 may range from about 45° to about 87° and is preferably 60°to 77°. The second portion 274 of the arcuate annular region 270, thatis the distal portion of the arcuate annular region 270 is positionedsuch that a line tangent to the curvature of the arcuate annular region270 at the second portion 274 slopes downwardly and outwardly at anangle of approximately 0° to 12°.

[0281] The combination of the annular region 264 and arcuate annularregion 270 should combine to position the second portion 274 of thearcuate annular region 260 in the manner set forth herein above. Thatis, the included angle 266 of the annular region 264 when combined withthe included angle 272 of the arcuate annular region 270 with the firstfrusto-conical region 264 spanning therebetween, positions the secondportion 274 of the arcuate annul region 270 in a manner such that thesecond frusto-conical region 276, which extends substantiallytangentially from the distal end of the second portion 274 of thearcuate annular region 270 extends outwardly and downwardly at an angleof about 0° to 12°. The second frusto-conical region 276 is of a lengthin a range from about 0.02 D to about 0.04 D and is preferably 0.03 D.Because the second frusto-conical region 276 extends substantiallytangentially from the second portion 274 of the arcuate annular region270, the second frusto-conical region 276 extends outwardly anddownwardly at an angle A3 in the range from approximately 0° to 12° withrespect to a horizontal plane formed by the planar inner region 260.

[0282] Adjoining an outer periphery of the second frusto-conical region268 is the lip 278 which is in the form of yet another frusto-conicalregion which extends outwardly and downwardly from the secondfrusto-conical region 276. The lip 278 is of a length of at least 0.01 Dand is preferably approximately 0.017 D. Further, the lip 278 extends atan angle A2 of no more than 45° from vertical, preferably approximately10° to 30° with respect to the vertical plane and more preferablyapproximately 25°.

[0283] At the transition between the second frusto-conical region 276and the lip 278 is a transition region 280. The transition region 280includes a radius of curvature R3 which is in the range of about 0.007 Dand 0.012 D and is preferably approximately 0.009 D with the centerpoint thereof being positioned a distance Y3 from the planar innerregion 260. Additionally, the transition region 280 has an includedangle A4 of approximately 48° to 80°.

[0284] There is shown in FIG. 29 yet another embodiment of a foodcontact article in accordance with the present invention. The containersof this invention may be formed as take-out containers, and arepresentative embodiment, a suitable take-out container, will now bedescribed in general with respect to FIG. 29 wherein the lid and basemay be formed as described in U.S. Pat. No. 5,377,860 which isincorporated herein by reference. While the container illustrated inFIG. 29 is oblong in configuration, the container may be round, oval,substantially rectangular or square as dictated by the contents whichare to be placed within the container. The container 290 is formed of abase or bottom portion 292 and a lid 294. The lid 294 includes radiallyextending opening tabs 296 which cooperate with the radially extendingopening tabs 298 of the base 292 in order to allow the consumer toreadily open the sealed container. The base 292 of the container 290includes a substantially planar bottom 300 and a substantiallyvertically extending peripheral sidewall 302. Integrally connected tothe upstanding sidewall 292 is a sealing brim 304 which is receivedwithin a cooperating sealing brim 306 of the lid 294.

[0285] The lid 294 includes a substantially planar top portion 308 and arim 310 extending about a periphery of the top portion 398. The rim 310is provided in order to enhance the strength of an extended volumeportion 312 of the lid 294. The rim 310 also serves to locate the base292 on the lid when the lid is used as a stand.

[0286] The extended volume portion 312 is formed by extension wall 314positioned about the perimeter of the rim 310 and extending downwardlytherefrom. The extension wall 314 is integrally formed with a horizontallid reinforcing ring 316 which is substantially parallel to the topportion 308 of the lid 294. The outer perimeter of the lid reinforcingring 316 is further integrally formed with the sealing brim 306. Also,extending radially outward from the sealing brim 306 is a secondhorizontal lid reinforcing ring 318 which extends substantially parallelto the top portion 308 as well.

[0287] Similarly, the base 292 includes a horizontal lid reinforcingring 320 which extends from the periphery of the sealing brim 304 foraiding in and maintaining the structural integrity of the sealing brim304 as well as the container 290 as a whole. In addition to thereinforcing ring 320, a step 322 may be provided about an upper portionof the peripheral sidewall 302 for preventing nested units from becomingjammed together due to excessive interpenetration when stacked andnested. Also, formed in an upper portion of the sidewall 302 areundercuts 324 which cooperate with detents 326, only one of which isillustrated in FIG. 29 at the integral connection between a brim 306 andlid reinforcing ring 316. The detents, when engaged in the undercuts324, provide an audible indication that the container is in fact sealed.Additionally, undercuts 328 may be provided in an outer periphery of thebrim 304 for receiving detents 330 formed in an outer portion of thebrim 306 for again providing an audible indication that the container issealed. While the container illustrated in FIG. 29 shows detents andundercuts formed in both the inner and outer portions of the brims 324and 306, respectively, it may be desired to provide respective detentsand undercuts on only one side of the brim or to provide no undercutsand detents on either side of the brim.

[0288] In a yet still further embodiment of this invention another bowlis illustrated in FIGS. 30 through 33. Throughout the followingdescription of the bowl of FIGS. 30 through 33, each of the dimensionsare referenced with respect to a given diameter D which, in accordancewith the present invention as illustrated is approximately 7.3 inches.However, the particular diameter of the containers is not a criticallimitation and is only set forth herein by way of example. It is therelationship between the various portions of the rim configuration whichare essential. The crowned imner region 340 in accordance with theillustrated embodiment in FIGS. 30 through 33, has a crown height Y5which is approximately 0.004 D to 0.012 D or preferably 0.008 D, andencompassing a radius X1 which is equal to approximately 0.2 D to 0.3 Dand preferably 0.25 D. Adjoining an outer periphery of the crowned innerregion 340 is a sidewall portion 342 including first annular region 344having a radius of curvature equal of approximately 0.05 D to 0.15 D andpreferably 0.11 D with the center point thereof being positioned atdistance Y1 from the tangency point between the crowned inner region 340and the first annular region 344. Included angle 346 of the firstannular region 344 is from about 45° to about 85° and is preferably 65°to 80° or approximately 72°. Adjoining the periphery of the firstannular region 344 in the sidewall portion 342 is a second annularregion 348 having a radius of curvature equal of approximately 0.8 D to1.2 D and preferably 0.96 D with the centerpoint thereof beingpositioned a distance Y2 from the tangency point between the crownedinner region 340 and the first annular region 344. The included angle ofarc A2 indicated generally at 350 of the second annular region 348 isfrom about 2° to 12° and is preferably 5° to 9° or approximately 7°.Adjoining the periphery of the second annular region 348 in the sidewallportion 342 is a third annular region 352 having a radius of curvatureequal to approximately 0.1 D to 0.2 D and preferably 0.15 D with thecenterpoint thereof being positioned a distance Y3 from the tangencypoint between the crowned inner region 340 and the first annular region344. Included angle 354 of the third annular region 352 is from about20° to 50° and is preferably 25° to 40° or approximately 33°. Adjoiningthe sidewall portion 342 is a flange portion 356 including a fourthannular region consisting of regions 358 and 360 which have the sameradius of curvature. Adjoining the third annular region 352 is a fourthannular region beginning with annular region 358 which extends to theuppermost bowl height and continuing with annular region 360 to bowldiameter D. Annular regions 358 and 360 are equivalent to one annularregion, flange portion 356 since both have the same radius of curvatureof approximately 0.02 D to 0.05 D and preferably 0.03 D with thecenterpoint thereof being positioned a distance Y4 from the tangencypoint between the crowned inner region 340 and the first annular region344. Included angle 362 of the fourth annular region 356 is from about45° to 85° and preferably 65° to 80° or approximately 73°.

[0289] Physical Properties, Heat Resistance and Food Contact Suitability

[0290]FIG. 34 shows rigidity versus current plate material costcomparisons for mica filled polypropylene plates versus competitorplastic disposable plates. “J” refers to mica filled polypropylene plateof this invention and “S” refers to polystyrene based plates such asthose currently manufactured by Solo Cup Company. Average plate calipersare indicated for each plate type and size. The left side of the diagramshows data for 8.75 inch plates whereby the J plate rigidity is aboutthree times higher than S at significantly reduced caliper and cost. Theright side of the diagram shows data for 10.25 inch plates whereby Jplated rigidity is more than seven times higher S at the same caliper.The open circle point corresponds to an estimated rigidity for the 10.25inch J plate that is scaled down in caliper so that plate material costsare equivalent to S.

[0291] The scaled J caliper X is calculated as X=(19 mil)(2.9 cents/3.8cents). The theoretical rigidity R1 at equivalent cost for thedownscaled caliper is calculated as:

(R1/R2)=(14.5 mil/19 mil) exp N

[0292] where R2 is the experimental rigidity at 19 mil and N=1.816 isthe caliper exponent value for the Dixie Superstrong 10.25 inch platedesign which is obtained from the general equation for rigidity:

R=(KE)TexpN

[0293] where E is Young's modulus, K is a shape constant, and T iscaliper. The data set forth in FIG. 34 demonstrate that the rigidity ofthe J plate of this invention is significantly higher at equivalent orlower material cost than commercial polystyrene polymer based plates.

[0294] In FIG. 35, the heat resistance performance for mica filledpolypropylene 10.25 inch plates (J), having an average caliper of 19 ml(J) is compared with (S) polystyrene based plates (S) of the same sizeand caliper. A measure of heat resistance is dynamic flexural storagemodulus E′, as measured with the Rheometrics Solids analyzer at 10rad/sec. Higher E′ values indicate increased stiffness and improveddimensional stability. Dynamic mechanical sprectroscopy is a commontechnique used for evaluation of viscoelastic properties of polymericmaterials with respect to temperature and input frequency (deformationtime scale). Dynamic mechanical properties of flat rectangular specimensof S plate material and PP/mica sheet of this invention were subjectedto flexural deformation at 10 rad/sec, using the Rheometrics SolidsAnalyzer RSAII instrument, manufactured by Rheometric Scientific, andequipped with a dual cantilever bending fixture. Temperature scans wereconducted at 0.05% strain using 2° C. temperature steps with a 0.5minute soak time at each temperature. From the time lag between inputstrain delivered by the driver motor and the stress output measured bythe transducer, values of material complex modulus E* are obtained. Theparameter E* is formally expressed as E*=E′+ iE″, where E′ is thestorage modulus (purely elastic term) and E″ is the loss modulus (purelyviscous term). The storage modulus E′ is defined as the stress in phasewith the strain divided by the strain, which gives a measure of theenergy stored and recovered per cycle. The loss modulus E″ is defined asthe stress 90 degrees out of phase with the strain divided by thestrain, which gives a measure of the energy dissipated per cycle. Theratio of loss modulus to storage modulus is commonly known as thedamping (tan delta) where delta is the phase angle between stress andstrain. The dynamic storage flexural modulus E′ is the operative measureof heat resistance performance, where higher values mean higherperformance. At ambient conditions (77° F.), E′ for mica filledpolypropylene plates of this invention is appreciably higher than for S.At 250° F., which corresponds to aggressive temperatures which arecommonly encountered in the microwave heating or cooking of greasyfoods, the heat resistance of J plates of this invention issignificantly superior to the plates manufactured by S, as furtherdemonstrated below in connection with microwave cooking trials. TABLE 20MICROWAVE COOKING TEST RESULTS FOR PLATES J AND S PLATE TYPE FOOD TYPE JS Donut Pass Sugar glazing sticks Broccoli/cheese Pass Significantlydeforms Pepperoni pizza Pass Moderate deformation, Staining Barbecuepork Slight stain Significant stain/warpage Pancake/syrup PassSignificant warpage Beans & pork Pass Significant warpage Butter Slightwarpage Significant warpage Bacon Moderate warpage Significant Localizedmelting, no leak warpage Rubbery plate flows and Sticks to glass tray

[0295] Microwaveability

[0296] Fort James Corporation (J) plate specimens of this invention andplates manufactured by Solo Cup Company (S) were tested in the microwave(Samsung model MW 8690) with a variety of foods. The highest powersetting (10) was used in all cases and cooking/heating times andprocedures corresponded to food manufacturer instructions on thepackages. Most tested foods were of the frozen microwaveable type andwere placed in a semi-thawed state directly on plates prior to cooking.When appropriate, a loose covering of wax paper was employed during thecooking process. After cooking, the plates were gently washed with warmwater and inspected. The following are the detailed test results whichare also summarized in above Table 20.

[0297] TEST #1 RESULTS-Sugar Glazed Donut

[0298] +E,uns J A large, oval shaped sugar glazed plain donut wasmicrowaved on the plate of this invention for 60 seconds. The sugarglazing melted, bubbled, and flowed on the plate. The boiling sugar andgrease mixture caused the bottom of the plate to feel very warm but theplate exhibited no warping, no staining, no softening, and nosoak-through. The plate was cool enough to be safely handled. Theresidue of the donut was easily washed off and the appearance of theused plate was excellent.

[0299] +E,uns S The bottom of the plate got hot and slightly deformedwith no soak-through, however, sugar stuck to the plate.

[0300] TEST #2 RESULTS-Broccoli With Cheese Sauce

[0301] +E,uns J Green Giant 10 oz. Broccoli with cheese sauce wasremoved from the flexible pouch and heated for five minutes in themicrowave on the plate with loose covering of wax paper. The cheesemelted and bubbled on the plate without sticking. The plate bottom waswarm, but no soak-through and no loss of dimensional stability wasobserved. After washing, no staining was observed and the appearance ofthe used plate was excellent.

[0302] +E,uns S The plate bottom got hot and significantly deformed withno soak-through.

[0303] TEST #3 RESULTS-Pepperoni pizza

[0304] +E,uns J Tombstone 7 oz. Pepperoni pizza was cooked on anuncovered plate for 4 minutes. The cheese melted and started bubblingabout halfway through the test. The molten cheese mingled with the hotliquid fat extruded from the pepperoni and dripped on the sides of thecrust onto the plate. No sticking, no soak-through, no staining, and noloss in plate dimensional stability was observed and the appearance ofthe used plate was excellent.

[0305] +E,uns S The plate bottom got hot and moderately deformed with nosoak-through. The greasy reddish stain from oil in pepperoni could notbe completely washed off.

[0306] TEST #4 RESULTS-Microwave Kid Meal:

[0307] Pork Rib Patties, Barbecue Sauce, Fries, Honey Corn Bread

[0308] +E,uns J A quick meal preparation simulation test was conductedusing a Swanson 7.2 oz. microwave kids' meal with ingredients consistingof partially cooked boneless pork rib patties, barbecue sauce, fries,and honey corn bread. The food was transferred from the compartmentedtray onto the plate. Sauce was spooned on top of the pork meat and wasallowed to drip on the sides of the patties and onto the plate. Thecornbread batter was spooned out and was placed on the plate next to thefries. The food was loosely covered with wax paper and cooked for 3.5minutes. Examination after microwaving showed that the cornbread wasfully cooked and there was no sticking or damage to the plate. The friesand pork meat with sauce caused no soak-through and no loss in platedimensional stability. Washing of plate revealed the presence of slightstaining from barbecue sauce. Overall, the appearance of the used platewas very good.

[0309] +E,uns S The plate bottom deformed mainly from pork meat withconsiderable staining from the barbecue sauce without soak-through.

[0310] TEST #5 RESULTS-Beans With Pork and Tomato Sauce

[0311] +E,uns J Beans with pork and tomato sauce (8 oz. Can) were placedon the plate, covered with wax paper and heated for 2 minutes nearboiling. The bottom of the plate got hot, but the rim was cool to touch.The hot plate bottom exhibited no bulging and also, when the hot foodplate was handled by the rim there was no perceived loss in dimensionalstability. No soak-through, no warping and no staining was observed. Theappearance of the plate was excellent.

[0312] +E,uns S The plate bottom became very hot and severely deformedwith no soak-through and when handled by the rim, the plate felt like ithad low rigidity.

[0313] TEST #6 RESULTS-Pancakes With Syrup and Precooked Bacon

[0314] +E,uns J In this test, Swanson microwave pancakes and baconbreakfast (4.5 oz. size) were used. The semi-thawed meal consisted ofthree pancakes and three partially, precooked bacon strips. The pancakesand bacon were removed from the tray in carton and placed on plate.Approximately 5 teaspoons of pancake syrup was spooned over the pancakesand the assembled meal was covered with wax paper and microwaved for 2minutes. Although the bottom of the plate got hot, the overall plateperformance was excellent, i.e. no warpage, no soak-through, no loss indimensional stability, and no staining. Some hot grease was exuded bythe bacon during crisping but there was no observed damage to the plate.The appearance of the used plate was excellent.

[0315] +E,uns S The plate bottom became hot and significantly deformed(especially in areas where bacon was placed), but no soak-through wasobserved and when handled by the rim, the plate felt soft.

[0316] TEST #7-Butter

[0317] +E,uns J Butter (5-tsp. chunk) was placed on the plate and wasloosely covered with wax paper and was microwaved for 3 minutes. Thebutter melted completely and covered the whole plate bottom. The butterbegan boiling toward the end of the test. The plate bottom got very hotand became slightly warped but no soak-through. The rim of the platefelt cool to touch enabling safe removal of the plate from the microwaveoven. A small portion of the butter became charred but was easily washedoff the plate. Overall plate performance was good.

[0318] +E,uns S The plate bottom became very hot and was significantlywarped but no soak-through was observed and the greasy film residuecould not be washed off completely. Plate felt soft and rubbery whenhandled by the rim.

[0319] TEST # RESULTS-Bacon

[0320] +E,uns J Three strips of raw, cured bacon were wrapped in threesheets of paper towel and cooked for 5 minutes. All of the bacon becamecrispy and about 20% of it was charred. The bottom of plate got very hotbut most of the rim area was relatively cool to the touch. Grease exudedfrom bacon and soaked through the towel. The grease pooled on the platebottom, side and on some rim areas. The grease which pooled in some rimregions caused localized melting of the plate but no holes were formed.The hot grease which pooled on plate bottom caused significant warpagebut no soak-through. Overall plate performance for Test #8 was lesssatisfactory than Test #7.

[0321] +E,uns S When the raw bacon was wrapped in paper toweling andcooked on the S plate, the bottom became very soft and stuck to theglass tray in the microwave. Under such hot grease conditions, theadhering polymer regions underwent localized melting and stretched whenthe plate was lifted off the glass tray. The plate was severely warpedbut no holes formed and no soak-through was noticed.

[0322] With the possible exception of raw bacon, the behavior of the Jplate of this invention in the microwave oven is considered excellentwith a variety of aqueous, greasy/fatty, sugary food combinations. Nounusual or off odors were detected during and after cooking for eachtype of food directly on the plate. The foregoing data demonstrates thesuperior properties of the plates of this invention.

[0323] Crack Resistance

[0324] Low temperature crack resistance of rigid plates is of paramountimportance when considering that product must survive during storage andshipping to point of sale. Normally, it is difficult to improve crackresistance or reduce brittleness of rigid polymeric materials withoutreducing the stiffness which is usually the case when introducingexcessive amounts of softer extensible materials such as polyethylenes,rubber modified resins and the like. In order to be successful inimparting crack resistance without significantly reducing stiffness,Rmust-add relativeLy-low amounts of polyethylene or rubber modifiedadditives, generally in the range of several to about 5 wt % . However,this invention shows that addition of low levels of polyethylene aloneis not sufficient to promote crack resistance whereby the desired resultis produced by a synergistic binary combination of polyethylene andTiO₂. Such low odor products have high crack resistance which rendersthem useful in the commercial sense.

EXAMPLES 63-70

[0325] There is provided in a still flrther aspect of the inventiontoughened, crack resistant articles. It has been found thatpolypropylene/mineral/polyethylene/titanium dioxide formulations withouta coupling agent resist cracking. Generally, the articles have thecomponents set forth in Table 21, in the amounts mentioned above in thesummary of the invention herein. In Table 21, it is demonstrated thatpolyethylene/titanium dioxide exhibit synergy in resisting cracking.TABLE 21 Low Temperature crack data for 9 inch plates made of PP/30%mica/10% CaCO₃ modified with various combinations of TiO₂, polyethylene,or coupling agent Coupling Example TiO₂ LLDPE HDPE Agent Percent Cracked# (wt %) (wt %) (wt %) (wt %)* plates at 0 F** 63 — 4 — — 100 (n = 5) 64— — — 2.5 100 (n = 5) 65 1.9 — — — 100 (n = 5) 66 — 4 — 2.5 100 (n = 5)67 1.9 0 0 2.5 100 (n = 5) 68 0.5 4 — 2.5  60 (n = 5) 69 0.5 4 0 0    0(n = 5) 70 0.5 0 4 0    0 (n = 10)

[0326] Crack resistance of Examples 63 through 70 was evaluated in thelaboratory according to method set forth below which was found useful asan investigative tool for optimizing the formulation with variouscombination of TiO₂, polyethylene, or coupling agent. A laboratoryprocedure was devised and used to evaluate the crack resistance ofplates. Specifically, following is a description of test instruments andassociated fixtures used to subject plates to a repeatable rim crushingforce. The model numbers of standard equipment used on this procedureare recited below and additional fixtures used in these tests wereemployed as follows:

[0327] Instron-Model #55R402 was used which was equipped with InstronEnvironmental Chamber Model #3111. The Instron environmentalchamber-Model #3111 was modified to control low temperatures with liquidnitrogen. It was equipped with a control solenoid mounted on the rear ofthe cabinet and an electronic control module mounted on the controlpanel assembly. The temperature within the chamber was controlled inrelationship to the setpoint on the front panel temperature dial. Athermocouple within the chamber provides feed back to the device. Amercury thermometer was placed in the chamber and oriented so thattemperature within the chamber was visible through an insulated glassdoor. It was monitored and adjusted to 0° C. using the panel temperaturedial.

[0328] A push rod was attached to the load cell of the instron and waspassed through an opening in the top of the environmental chamber. Acircular metal device measuring 100 mm in diameter and 10 mm in thickwas attached to the end of the push rod inside the chamber. Thiscircular metal device was used to contact the edge of a plastic plateduring testing.

[0329] The plate support fixture was placed on a circular metal basesupport which measured 140 mm in diameter by 14 mm thick. This metalbase support was located just above the inside floor of theenvironmental chamber. It was attached to a support rod that passesthrough the floor of the environmental chamber and attached to the baseof the instron. Centering stops were provided on the metal base supportso that the plate support fixture could be repeatedly placed at the samelocation in the environmental cabinet.

[0330] The plate support fixture is constructed of 5-mm thick sheets ofplexiglas. The main base of this fixture measures 100×125 mm. The 125-mmdimension represents the width of the front of the mixture. The edge ofthe 125 mm side of a second plexiglas panel measuring 160×125 mm waspermanently attached to the plexiglas main base. This panel was attachedat a 90° angle to the main base and 35 mm in from the front edge. An Lshaped plexiglas component was attached to the main base behind andparallel to the permanent panel by thumbscrews. Two 20-mm long slotswere provided in the base of the L shaped component to allow attachmentand provide movement for adjustment to hold the test plate. The shortleg or base of the L shaped component faces the rear of the fixture. Ablock measuring 40×25×15 mm thick was permanently attached at the uppermost end at the center of the L shaped component. This block is locatedon the front side of the moveable component or just opposite the shortleg of the L shaped component, while an adjustable plate stop wasattached to one side of the moveable L shaped component.

[0331] The methodology for testing the crack resistance of plates was asfollows. The test plate was secured in a vertical position on edge inthe plate support fixture. The bottom of the test plate was placedagainst the permanently attached plexiglas panel of the plate supportfixture. The thumbscrews were loosened on the moveable portion of theplate support fixture. The L shaped moveable component was moved towardthe plate. The plate was held in a vertical position by the fixedplexiglas panel and the block which was attached to the wall of the Lshaped moveable component.

[0332] The plate stop located on the L shaped moveable component wasadjusted so that the center of the plate would align with the center ofthe plate support fixture. The plate support fixture along with the testplate secured in a vertical position was placed on the metal basesupport in the environmental chamber. The instron was adjusted so thatthe push rod crush assembly was located 0.5 inches above the plate edge.

[0333] Prior to the test, the environmental chamber was adjusted to 0°F. After placement of the plate support fixture along with the testplate secured in a vertical position in the environmental chamber, thechamber had to re-establish 0° F. This time period was about 30 seconds.After re-establishment of the test temperature, the plate wasconditioned for an additional five minutes prior to the test.

[0334] The crosshead speed of the instron was set at 40 inches perminute. After the five minute conditioning time period, the instron wasactivated and the edge crushing force applied. A set of five or a set often replicate plates was tested for each condition The total number ofplates tested and the total number plates showing rim crack failure foreach condition tested are reported in Table 21. In addition, thepercentage of plates which cracked was calculated as shown above.

[0335] The above formulations for crack resistance testing werecompounded in the temperature range of 400 to about 425° F. oncommercial Banbury equipment using batch sizes in the range of 150-200lb. and nominal mixing times of 3 min. followed by underwaterpelletizing.

[0336] Pellets were subsequently extruded at 370° F. as cast sheets inthe range of 18 mil. Sheet line conditions also included a screw RPMvalue of 100, a chill roll temperature of 130° F. Plates weresubsequently vacuum thermoformed using a female mold, trimmed, andthereafter tested for crack resistance.

[0337] Data on Examples 63 through 65 show that presence of TiO₂,polyethylene, or coupling agent alone is not sufficient to promote crackresistance of plates comprised of PP/mica/CaCO₃. In addition, data onExamples 66 and 67 show that binary combinations of polyethylene withcoupling agent or TiO₂ with coupling agent are two cases which are alsonot sufficient for imparting crack resistance. Futhermore, the tertiarycombination of TiO₂, polyethylene, and coupling agent (Example 68) alsodoes not impart sufficient crack resistance, as evidenced by themajority of samples which exhibit cracking. Rather, the useful additivepackages of this invention (Examples 69 and 70) comprises the binarysystem of polyethylene (either LLDPE or HDPE) with at least 0.5 wt %TiO₂ whereby crack resistance is excellent as evidenced by no crackedsamples.

EXAMPLES 71-78

[0338] Additional plates were fabricated in accordance with theforegoing procedures and compositions; crack testing results appear inTable 22 below TABLE 22 Crack Data and Physical Properties for VariousCompounded Formulations Base Formulation: PP/30% Mica/10% CaCO₃ MeltFlexural Formulation Flow Filler Modulus 9″ Plate Product Crack DataTiO₂ PE Coupling g/10 min. Content Tangent Rigidity Weight @ 0° F.Example (wt. %) (4 wt. %) Agent* @ 230° C. (Wt. %) (psi) (grams/0.5″)(grams) (#Cracked Total) 71 0 LLDPE No 1.45 39.4 505,000 288 19.3 5/5 721.9 LLDPE No 1.64 40.6 581,600 422 23.13 0/5 73 1.2 LLDPE No 2.05 39.8578,500 385 22.12 0/5 74 0.5 LLDPE No 1.77 38.6 487,500 286 20.65 0/5 751.9 HDPE No 1.5 40.6 637,500 436 22.70 1/5 76 1.9 0 Yes 1.9 39.0 717,585417 21.25 5/5 77 1.9 LLDPE Yes 1.6 39.6 494,000 391 21.6 5/5 78 1.9 0Yes 1.2 40.3 593,000 353 20.8 5/5

[0339] In a still further aspect of the invention, food contact articlesare provided by way of preparing a melt-compounded composition with fromabout 40 to 90 percent of a polypropylene polymer, about 10 to about 50percent by weight of a mineral filler and optionally an effective amountof an odor-reducing compound. The melt-compounded composition isextruded into a sheet and formed into a food contact article and ischaracterized by a relative aroma index, relative to a compositioncontaining 30 weight percent mica only, of less than about 0.75;preferably less than about 0.6. The relative aroma index is thus definedsimilarly as above; however, relative to a mica composition without anodor suppressing compound such as calcium carbonate. Stated another way,the relative aroma index is determined in the same way as the odor indexutilizing the AromaScan®-device as noted above or other suitableinstrument, except a 30 wt. % mica filled composition is used as thereference (or denominator) compound. In equation form,${{Relative}\quad {Aroma}\quad {Index}} = \frac{\begin{matrix}{{{Average}\quad {readings}\quad {of}\quad {pellets}\quad {including}}\quad} \\{{a\quad {primary}\quad {mineral}\quad {filler}\quad {and}}\quad} \\{{optionally}\quad {including}\quad {calcium}} \\{{carbonate}\quad {or}\quad {other}\quad {odor}\quad {suppressing}} \\{compound}\end{matrix}\quad}{\begin{matrix}{{Average}\quad {readings}\quad {of}\quad {pellets}\quad {including}} \\{30\quad {wt}\quad \% \quad {mica}\quad {without}\quad {an}\quad {odor}} \\{{suppressing}\quad {basic}\quad {compound}}\end{matrix}}$

[0340] Thus, a composition consisting essentially of 30% talc, 10%calcium carbonate and the balance polypropylene would have a relativearoma index, relative to a 30% by weight mica composition of:${{Relative}\quad {Aroma}\quad {Index}} = \frac{\begin{matrix}{{{Average}\quad {readings}\quad {of}\quad 30\% \quad {talc}},{10\%}} \\{{{{calcium}\quad {carbonate}},{60\%}}\quad} \\{{polypropylene}\quad {composition}}\end{matrix}}{\begin{matrix}{{{Average}\quad {readings}\quad {of}\quad 30\% \quad {mica}},} \\{70\% \quad {polypropylene}\quad {composition}}\end{matrix}}$

[0341] The invention also includes: (a) preparing a melt-compoundedcomposition including from about 90 percent by weight of a polypropylenepolymer, from about 10 to about 50 percent by weight of a primarymineral filler and optionally an effective odor-reducmg amount of abasic or optionally acidic organic or inorganic compound; (b) extrudingthe melt-compounded composition into a sheet; and (c) forming a foodcontact article from the sheet, wherein the melt compounded compositionexhibits a relative aroma index of 0.75 or less. Particularly preferredprimary mineral fillers include talc, kaolin, bentonite andwollastonite.

[0342] While the invention has been described in its various aspects forpurposes of illustration, modifications to particular embodiments withinthe spirit and scope of the present invention will be readily apparentto those of skill in the art. The invention is defined in the appendedclaims.

What we claim is:
 1. A method of preparing a microwaveable,mineral-filled polypropylene food contact article comprising: (a)preparing a melt-compounded composition comprising from about 40 toabout 90 percent by weight of a polypropylene polymer, from about 10 toabout 50 percent by weight of a primary mineral filler and an effectiveodor-reducing amount of a basic organic or inorganic compound, saidmelt-compounded composition exhibiting an odor index of less than 0.75;(b) extruding said melt-compounded composition into sheet form; and (c)forming said food contact article from said sheet, wherein said basicorganic or inorganic compound is operative to reduce undesirable odorsin said melt-compounded composition to the aforesaid odor index value of0.75 or less.
 2. The method according to claim 1 , wherein said primaryfiller is selected from the group consisting of mica, clays, siliceousmaterials, ceramics, glass, sulfate minerals, and mixtures thereof. 3.The method according to claim 2 , wherein said primary filler is talc.4. The method according to claim 3 , wherein said primary filler iskaolin.
 5. The method according to claim 1 , wherein said primary filleris selected from the group consisting of mica, talc, kaolin, bentonite,wollastonite, milled glass fiber, glass beads, hollow glass beads,silica whiskers, silicon carbide whiskers and mixtures thereof.
 6. Themethod according to claim 5 , wherein said primary filler is bentonite.7. The method according to claim 5 , wherein said primary filler iswollastonite.
 8. The method according to claim 1 , wherein said basicorganic or inorganic compound comprises the reaction product of analkali metal or alkaline earth element with carbonates, phosphates,carboxylic acids as well as alkali metal and alkaline earth elementoxides, hydroxides, or silicates and basic metal oxides, includingmixtures of silicon dioxide with one or more of the following oxides:magnesium oxide, calcium oxide, barium oxide, and mixtures thereof. 9.The method according to claim 8 , wherein the basic organic or inorganiccompound is selected from the group consisting of calcium carbonate,sodium carbonate, potassium carbonate, barium carbonate, aluminum oxide,sodium silicate, sodium borosilicate, magnesium oxide, strontium oxide,barium oxide, zeolites, sodium citrate, potassium citrate, sodiumcitrate, calcium stearate, potassium stearate, sodium phosphate,potassium phosphate, magnesium phosphate, mixtures of silicon dioxidewith one or more of the following oxides: magnesium oxide, calciumoxide, barium oxide, and mixtures of one or more of the above.
 10. Themethod according to claim 9 , wherein the basic inorganic compound isselected from the group consisting of calcium carbonate, sodiumcarbonate, potassium carbonate, barium carbonate, aluminum oxide, sodiumsilicate, sodium borosilicate, magnesium oxide, strontium oxide, bariumoxide, zeolites, sodium phosphate, potassium phosphate, magnesiumphosphate, mixtures of silicon dioxide with one or more of the followingoxides: magnesium oxide, calcium oxide, barium oxide, and mixtures ofone or more of the basic inorganic compounds set forth above, whereinthe amount of the basic inorganic compound is from about 2 to about 20weight percent of said article.
 11. The method according to claim 10 ,wherein said basic inorganic compound is calcium carbonate.
 12. Themethod according to claim 11 , wherein calcium carbonate is present insaid article from about 5 to about 20 weight percent.
 13. The methodaccording to claim 9 , wherein said basic organic compound is selectedfrom the group consisting of sodium stearate, calcium stearate,potassium stearate, sodium citrate, potassium citrate, and mixtures ofthese wherein the amount of the basic organic compound is from about 0.5to about 2.5 weight percent of said article.
 14. The method according toclaim 1 , wherein said composition exhibits an odor index of less thanabout 0.6.
 15. The method according to claim 1 , wherein said article isa bowl or a plate.
 16. The method according to claim 1 , wherein saidarticle is formed, or thermoformed by application of pressure, byapplication of vacuum, or by a combination of vacuum and pressure, intothe shape of a container; said container exhibiting a melting point ofno less than about 250° F., said container being dimensionally stableand resistant to grease, sugar and water at temperatures up to at least220° F. and of sufficient toughness to be resistant to cutting byserrated polystyrene flatware.
 17. The method according to claim 16 ,wherein said article has at least one micronodular food contact surface.18. The method according to claim 17 , wherein said micronodular surfaceis produced through vacuum thermoforming on the side opposite saidmicronodular food contact surface.
 19. The method according to claim 18, wherein said micronodular food contact surface exhibits a surfacegloss of less than about 35 at 75° as measured by TAPPI method T480-OM92.
 20. The method according to claim 20 , wherein said micronodularfood contact surface exhibits a Parker Roughness Value of at least about12 microns.
 21. The method according to claim 1 , wherein saidpolypropylene polymer is selected from the group consisting of:isotactic polypropylene, co-polymers of propylene and ethylene whereinthe ethylene moiety is less than about 10 percent of the units making upthe polymer and mixtures thereof.
 22. The method according to claim 21 ,wherein said polymer is isotactic polypropylene and has a melt-flowindex from about 0.3 to about
 4. 23. The method according to claim 22 ,wherein said polypropylene has a melt flow index of about 1.5.
 24. Themethod according to claim 1 , wherein said composition further includesa polyethylene component.
 25. The method according to claim 24 , whereinsaid polyethylene is selected from the group consisting of HDPE, LDPE,LLDPE, MDPE and mixtures thereof.
 26. The method according to claim 24 ,wherein said polyethylene component comprises HDPE.
 27. Themicrowaveable article according to claim 24 , wherein said polyethylenecomponent comprises LLDPE.
 28. The method according to claim 24 ,wherein said article ftirther includes titanium dioxide.
 29. Themicrowaveable article according to claim 1 , wherein said articleexhibits a melting point of from about 250 to about 330° F.
 30. Themethod according to claim 1 , wherein said article is substantially freefrom volatile C8 and C9 organic ketones.
 31. The method according toclaim 1 , wherein said article is prepared from a melt-compoundedpolypropylene mineral filled composition which is produced at a processmelt temperature of less than about 425° F.
 32. The method according toclaim 31 , wherein said article is produced from a melt-compoundedpolypropylene mineral filled composition which is prepared at atemperature below about 400° F.
 33. The method according to claim 31 ,wherein said article is thermoformed from an extruded sheet producedfrom a melt-compounded polypropylene mineral filled composition whichwas prepared at a process melt temperature of less than about 425° F.34. The method according to claim 1 , wherein said melt processedpolypropylene mineral filled composition is melt-compounded in anitrogen atmosphere.
 35. A microwaveable, mineral filled polypropylenefood contact article formed from a sheet of a melt-compoundedcomposition comprising from about 40 to about 90 percent by weight of apolypropylene polymer, from about 10 to about 50 percent by weight of aprimary mineral filler and an effective odor-reducing amount of a basicorganic or inorganic compound operative to impart an odor index of lessthat about 0.75 to said melt-compounded composition.
 36. Themicrowaveable article according to claim 35 , wherein the basic organicor inorganic compound is selected from the group consisting of calciumcarbonate, sodium carbonate, potassium carbonate, barium carbonate,aluminum oxide, sodium silicate, sodium borosilicate, magnesium oxide,strontium oxide, barium oxide, zeolites, sodium citrate, potassiumcitrate, calcium stearate, potassium stearate, sodium phosphate,potassium phosphate, magnesium phosphate, mixtures of silicon dioxidewith one or more of the following oxides: magnesium oxide, calciumoxide, barium oxide, and mixtures of one or more of the above.
 37. Themicrowaveable article according to claim 36 , wherein the basicinorganic compound is selected from the group consisting of calciumcarbonate, sodium carbonate, potassium carbonate, barium carbonate,aluminum oxide, sodium silicate, sodium borosilicate, magnesium oxide,strontium oxide, barium oxide, zeolites, sodium phosphate, potassiumphosphate, magnesium phosphate, mixtures of silicon dioxide with one ormore of the following oxides: magnesium oxide, calcium oxide, bariumoxide, and mixtures of one or more of the basic inorganic compounds setforth above, wherein the amount of the basic inorganic compound is fromabout 5 to about 20 weight percent of said article.
 38. Themicrowaveable article according to claim 37 , wherein said basicinorganic compound is calcium carbonate.
 39. The microwaveable articleaccording to claim 37 , wherein calcium carbonate is present in saidarticle from about 8 to about 12 weight percent.
 40. The microwaveablearticle according to claim 35 , wherein said basic organic compound isselected from the group consisting of sodium stearate, calcium stearate,potassium stearate, sodium citrate, potassium citrate, and mixtures ofthese wherein the amount of the basic organic compound is from about 0.5to about 2.5 weight percent of said article.
 41. The article ofmanufacture according to claim 35 , in the form of a plate having asubstantially planar center portion; a first rim portion extendingoutwardly therefrom, said first rim portion being upwardly convex andsubtending a first arc with a first radius of curvature; a second rimportion joined to said first rim portion, and extending outwardlytherefrom, said second rim portion being downwardly convex, subtending asecond arc with a second radius of curvature; a third rim portion joinedto said second rim portion and extending outwardly therefrom, said thirdrim portion being downwardly convex, subtending a third arc with a thirdradius of curvature as well as a tangent thereto which is substantiallyparallel to the plane of said substantially planar center section; and,a fourth rim portion joined to said third rim portion and extendingoutwardly therefrom, said fourth rim portion being downwardly convexsubtending a fourth arc having a fourth radius of curvature, wherein thelength of said second arc of said second rim portion is substantiallyless than the length of said fourth arc of said fourth rim portionwhich, in turn, is substantially less than the length of said first arcof said first rim portion and wherein said fourth radius of curvature ofsaid fourth rim portion is less than said third radius of curvature ofsaid third rim portion which , in turn, is less than said second radiusof curvature of said second rim portion and wherein the angle of saidfirst arc is greater that about 55 degrees and the angle of said thirdarc is greater than about 45 degrees.
 42. The plate according to claim41 , wherein the angle of said fourth arc is less than about 75 degrees.43. The plate according to claim 41 , wherein the length of said firstarc is substantially equivalent to the length of said third arc and saidfirst radius of curvature of said first arc is substantially equivalentto said third radius of curvature of said third arc.
 44. The plateaccording to claim 41 , wherein the height of the center of curvature ofsaid first rim portion above the plane of said substantially planarportion is substantially less than the distance by which the center ofcurvature of said rim portion is below the plane of said substantiallyplanar portion.
 45. The plate according to claim 41 , wherein thehorizontal displacement of the center of curvature of said second rimportion from the center of curvature of said first rim portion is atleast about twice said first radius of curvature of said first rimportion.
 46. The plate according to claim 41 , wherein said height ofthe center of curvature of said third rim portion above the plane ofsaid substantially planar portion is less than the height of the centerof curvature of said fourth rim portion above the plane of saidsubstantially planar portion.
 47. The plate according to claim 41 ,wherein the horizontal displacement of the center of curvature of saidsecond rim portion is located outwardly from the center of curvature ofboth said third and fourth rim portions.
 48. The plate according toclaim 41 , wherein the height of the center of curvature of said thirdrim portion above the plane of said substantially planar portion is lessthan about 0.75 times the radius of curvature of said fourth rim portionand the height of the center of curvature of said fourth rim portionabove the plane of said substantially planar portion is at least about0.4 times said first radius of curvature of said first rim portion. 49.A low temperature process for preparing a polypropylene mineral filledmelt-compounded composition comprising a basic odor suppressing agent,from about 40 to about 90 percent by weight of a polypropylene polymerand from about 10 to about 50 percent by weight of a mineral filler saidmelt-compounded composition exhibiting an odor index of less than about0.75 said process comprising the sequential steps of: (a) preheating apolypropylene polymer while maintaining the polymer below a maximumtemperature of about 350OF; followed by (b) admixing a mineral filler tosaid pre-heated polymer in an amount from 10 to about 50 percent byweight based on the combined weight of resin and filler; followed by (c)extruding said mixture.
 50. The process according to claim 49 , whereinsaid maximum temperature of Step (a) is about 260° F.
 51. The processaccording to claim 49 , wherein said polymer is melted through theapplication of shear.
 52. The process according to claim 49 , whereinsaid polypropylene polymer is preheated prior to said admixing stepexternally to the vessel in which said step of admixing the mica takesplace.
 53. The process according to claim 49 , wherein the duration ofStep (b) is a maximum of about 5 minutes.
 54. The process according toclaim 49 , wherein the duration of Step (b) is a maximum of about 3minutes.
 55. The process according to claim 49 , wherein said basic odorsuppressing agent is added to the mixture simultaneously with saidmineral filler in step (b) of the process.
 56. The process according toclaim 55 , wherein said steps of preheating said polymer and admixingsaid mineral filler and odor suppressing compound to said resin arecarried out in a batch mode in a mixing chamber provided with a pair ofrotating rotors.
 57. The process according to claim 49 , wherein saidodor suppressing compound is a basic organic or inorganic compoundcomprising the reaction product of an alkali metal or an alkaline earthelement with carbonates, phosphates, carboxylic acids, as well as alkalimetal and alkaline earth element oxides, hydroxides or silicates, basicmetal oxides including mixtures of silicon dioxide with one or more ofthe following oxides: magnesium oxide, calcium oxide, barium oxide, andmixtures of one or more of the organic or inorganic compounds set forthabove.
 58. The process according to claim 57 , wherein the basic organicor inorganic compound is selected from the group consisting of calciumcarbonate, sodium carbonate, potassium carbonate, barium carbonate,aluminum oxide, sodium silicate, sodium borosilicate, magnesium oxide,strontium oxide, barium oxide, zeolites, sodium citrate, potassiumcitrate, sodium stearate, calcium stearate, potassium stearate, sodiumphosphate, potassium phosphate, magnesium phosphate, mixtures of silicondioxide with one or more of the following oxides: magnesium oxide,calcium oxide, barium oxide, and mixtures of one or more of the organicor inorganic compounds set forth above.
 59. The process according toclaim 58 , wherein the basic inorganic compound is selected from a groupconsisting of calcium carbonate, sodium carbonate, potassium carbonate,barium carbonate, aluminum oxide, sodium silicate, sodium borosilicate,magnesium oxide, strontium oxide, barium oxide, zeolites, sodiumphosphate, potassium phosphate, magnesium phosphate, mixtures of silicondioxide with one or more of the following oxides: magnesium oxide,calcium oxide, barium oxide, and mixtures of one or more of the basicinorganic compounds set forth above and wherein the amount of the basicinorganic compound is from about 5 to about 20 weight percent of thecomposition.
 60. A crack-resistant, food contact article having a wallthickness from about 10 to about about 80 mils consisting essentially offrom about 40 to about 90 percent by weight of a polypropylene polymer,from about 10 to about 60 percent by weight of a mineral filler, fromabout 1 to about 15 percent by weight polyethylene, from about 0.1 toabout 5 weight percent titanium dioxide and optionally including a basicorganic or inorganic compound comprising the reaction product of analkali metal or alkaline earth element with carbonates, phosphates,carboxylic acids as well as alkali metal and alkaline earth elementoxides, hydroxides, or silicates and basic metal oxides, includingmixtures of silicon dioxide with one or more of the following oxides:magnesium oxide, calcium oxide, barium oxide, and mixtures thereof. 61.The crack-resistant food contact article according to claim 60 , whereinsaid basic organic or inorganic compound comprises calcium carbonate andsaid calcium carbonate is present in an amount of from about 5 to about20 weight percent.
 62. The crack-resistant, food contact articleaccording to claim 60 wherein polyethylene is present from about 2.5 toabout 15 percent by weight.
 63. The crack-resistant, food contactarticle according to claim 62 , wherein polyethylene is present fromabout 4 to about 5 weight percent.
 64. The crack-resistant, food contactarticle according to claim 60 , wherein titanium dioxide is present fromabout 0.1 to about 3 weight percent.
 65. The crack-resistant, foodcontact article according to claim 64 , wherein titanium dioxide ispresent from about 0.25 to about 2 percent by weight.
 66. Thecrack-resistant, food contact article according to claim 60 whereintitanium dioxide is present in an amount of at least about 0.5 percentby weight.
 67. The crack-resistant, food contact article according toclaim 60 , wherein said article has a wall caliper of from about 110 toabout 50 mils.
 68. The crack-resistant, food contact article accordingto claim 67 , wherein said article has a wall caliper of from about 15to about 25 mils.
 69. The crack-resistant, food contact articleaccording to claim 60 , wherein said rineral filler is mica.
 70. Thecrack-resistant, food contact article according to claim 60 , whereinsaid polypropylene polymer is isotactic polypropylene.
 71. Thecrack-resistant, food contact article according to claim 70 , whereinsaid isotactic polypropylene has a melt index of from about 0.3 to about4.
 72. The crack-resistant, food contact article according to claim 71 ,wherein said isotactic polypropylene has a melt flow index of about 1.5.73. The crack-resistant, food contact article according to claim 60 ,wherein said polyethylene is HDPE.
 74. The crack-resistant, articleaccording to claim 60 , wherein said polyethylene is LLDPE.
 75. A methodof preparing a microwaveable, mineral-filled polpropylene food contactarticle comprising: (a) preparing a melt-compounded compositioncomprising from about 40 to about 90 percent by weight of apolypropylene polymer and from about 10 to about 50 percent by weight ofa mineral filler and optionally an effective amount of an odor-reducingcompound; said melt-compounded composition exhibiting a relative aromaindex, relative to a 30 weight percent mica composition of less than0.75; (b) extruding said melt-compounded composition into sheet form;and (c) forming said food contact article from said sheet.
 76. Themethod according to claim 75 , wherein said mineral filler is selectedfrom the group consisting of mica, clays, siliceous materials, ceramics,glass, ceramics, sulfate minerals, and mixtures thereof.
 77. The methodaccording to claim 76 , wherein said mineral filler is selected from thegroup consisting of mica, talc, kaolin, bentonite, wollastonite, milledglass fiber, glass beads, hollow glass beads, silica whiskers, siliconcarbide whiskers and mixtures thereof.
 78. The method according to claim77 , wherein said mineral filler is talc.
 79. The method according toclaim 77 , wherein said mineral filler is kaolin.
 80. The methodaccording to claim 77 , wherein said mineral filler is bentonite. 81.The method according to claim 77 , wherein said mineral filler iswollastonite.
 82. The method according to claim 75 , wherein saidmelt-compounded composition includes a basic odor suppressing compound.83. The method according to claim 82 , wherein said basic odorsuppressing compound is a carbonate or hydroxide of an alkali metal oran alkaline earth element.
 84. The method according to claim 83 ,wherein said basic odor suppressing compound is calcium carbonate. 85.The method according to claim 75 , wherein said melt-compoundedcomposition exhibits a relative aroma index, relative to a 30 weightpercent mica, polypropylene composition of less than about 0.6.
 86. Amethod of preparing a microwaveable, mineral-filled polypropylene foodcontact article comprising: (a) preparing a melt-compounded compositioncomprising from about 40 to about 90 percent by weight of apolypropylene polymer, from about 10 to about 50 percent by weight of aprimary mineral filler and optionally an effective odor-reducing amountof a basic or optionally acidic organic or inorganic compound,; (b)extruding said melt-compounded composition into sheet form; and (c)forming said food contact article from said sheet, wherein themelt-compounded composition exhibits a relative aroma Index value of0.75 or less.
 87. The method according to claim 86 , wherein saidprimary mineral filler is talc.
 88. The method according to claim 86 ,wherein said primary mineral filler is kaolin.
 89. The method accordingto claim 86 , wherein said primary mineral filler is bentonite.
 90. Themethod according to claim 86 , wheren said primary mineral filler iswollastonite.